Four acinetobacter baumannii lipopolysaccharide inner core oligosaccharide fragments and methods of synthesis thereof

Abstract

This invention relates to the field of chemical synthesis, specifically to a core oligosaccharide fragment of lipopolysaccharide in Acinetobacter baumannii ATCC 17904 serotype and its synthesis method. This invention synthesizes four oligosaccharide molecules of varying lengths and structures (branched or linear), all possessing antigenicity. Furthermore, the branched trisaccharides included in their structures are common to the core oligosaccharides within the cell walls of different serotypes of Acinetobacter baumannii. Therefore, these four oligosaccharide fragments can be used to prepare immunoassay reagents to detect the presence of corresponding antibodies in test samples, i.e., to determine the presence of infection caused by Acinetobacter baumannii. Further, these four oligosaccharide fragments can be conjugated with suitable proteins to form glycoconjugates, which can then be used to prepare vaccines for the treatment or prevention of diseases caused by Acinetobacter baumannii.

Description

Technical Field

[0001] This invention relates to the field of chemistry, specifically to four core oligosaccharide fragments of serum-type lipopolysaccharide from Acinetobacter baumannii ATCC 17904 and their synthesis methods. Background Technology

[0002] Acinetobacter baumannii, also known as Acinetobacter baumannii, is a Gram-negative bacterium, a strictly aerobic, non-lactose-fermenting opportunistic pathogen. It lacks flagella, has low mobility, but is extremely resilient and widely distributed in nature. *A. baumannii* primarily causes acute pneumonia and meningitis in humans, and is a significant pathogen in hospital-acquired infections. The resistance rate of *A. baumannii* to commonly used antibiotics is increasing year by year. Recently, even fully drug-resistant *A. baumannii* has emerged in China, causing serious concern among clinicians and microbiologists. In 2017, the World Health Organization (WHO) released a list of bacteria urgently requiring the development of new antibiotics, with carbapenem-resistant *A. baumannii* listed as "extremely important," demonstrating the serious threat *A. baumannii* poses to human health and public health. Therefore, there is an urgent need to develop new drugs and vaccines for the treatment or prevention of *A. baumannii*. Summary of the Invention

[0003] In view of this, the present invention provides an oligosaccharide fragment comprising a compound of the structure shown in formula (1), formula (2), formula (3) or formula (4) or a pharmaceutically acceptable salt thereof:

[0004]

[0005] The present invention also provides a glycoconjugate, which is formed by conjugating the above-mentioned oligosaccharide fragments with a protein.

[0006] The present invention also provides the use of the glycoconjugate in the preparation of a vaccine for the prevention or treatment of diseases caused by Acinetobacter baumannii infection.

[0007] Furthermore, the diseases include one or more of bacteremia, pneumonia, meningitis, peritonitis, endocarditis, urinary tract infections, and skin infections.

[0008] The present invention also provides an immunoassay reagent comprising the above-mentioned oligosaccharide fragment; and a method for detecting Acinetobacter baumannii infection, wherein the immunoassay reagent is used to detect whether antibodies binding the oligosaccharide fragment are present in the sample to be tested.

[0009] Furthermore, the samples include blood samples.

[0010] Another aspect of the present invention provides a method for synthesizing the above-mentioned four oligosaccharide fragments.

[0011] The synthetic method for preparing compound 1 includes the following steps:

[0012] S1.1. Using compounds 9 and 7 as starting materials, compound 5 was obtained by glycosylation reaction;

[0013] S1.2. Compound 5 is subjected to an allyl group removal reaction to obtain compound 10;

[0014] S1.3. Compound 10 and compound 8a are glycosylated to obtain compound 13;

[0015] S1.4. Compound 13 is subjected to a desilication reaction to obtain compound 14;

[0016] S1.5. Compound 14 was subjected to deisopropylidene ketalization, saponification, and catalytic hydrogenation reduction to obtain compound 1 as shown.

[0017] The synthetic method for preparing compound 2 includes the following steps:

[0018] S2.1. Using compounds 9 and 7 as starting materials, compound 5 was obtained by glycosylation reaction;

[0019] S2.2. Compound 5 is subjected to an allyl group removal reaction to obtain compound 10;

[0020] S2.3. Compound 10 and compound 8a are subjected to a glycosylation reaction to obtain compound 13;

[0021] S2.4. Compound 13 is subjected to a desilication reaction to obtain compound 14;

[0022] S2.5. Compound 14 is subjected to an isopropyl ketal reaction to yield compound 15;

[0023] S2.6. Compound 15 and compound 7 are glycosylated to obtain compound 16;

[0024] S2.7. Compound 16 is subjected to desilication, deisopropyl ketalization, saponification and catalytic hydrogenation reduction to obtain compound 2.

[0025] The synthetic method for preparing compound 3 includes the following steps:

[0026] S3.1. Using compound 9 and compound 8b as starting materials, compound 6 was obtained by glycosylation reaction;

[0027] S3.2. Compound 6 is subjected to an allyl group removal reaction to obtain compound 17;

[0028] S3.3. Compound 17 and compound 8a are glycosylated to obtain compound 19;

[0029] S3.4. Compound 19 is subjected to a desilication reaction to obtain compound 20;

[0030] S3.5. Compound 20 and compound 21 are subjected to a glycosylation reaction to obtain compound 22;

[0031] S3.6. Compound 22 is subjected to a desilication reaction to obtain compound 23;

[0032] S3.7. Compound 23 is subjected to TEMPO oxidation and methyl esterification to obtain compound 24;

[0033] S3.8. Compound 24 was subjected to deisopropylidene ketalization, saponification and catalytic hydrogenation reduction to obtain compound 3.

[0034] The synthetic method for preparing compound 4 includes the following steps:

[0035] S4.1. Using compounds 9 and 7 as starting materials, compound 5 was obtained by glycosylation reaction;

[0036] S4.2. Compound 5 was subjected to desilication and isopropylidene ketal reaction sequentially to obtain compound 12;

[0037] S4.3. Compound 12 and compound 7 are glycosylated to obtain compound 25;

[0038] S4.4. Compound 25 was subjected to desilication, deisopropylidene ketalization, and full acetylation reactions to obtain compound 26;

[0039] S4.5. Compound 26 is subjected to an allyl group removal reaction to yield compounds 27 and 28;

[0040] S4.6. Compound 4 is obtained by saponification and catalytic hydrogenation reduction of compounds 27 and 28.

[0041] Beneficial technical effects

[0042] The technical solution of this invention takes into account that the core oligosaccharide in the cell wall of Acinetobacter baumannii has significant structural novelty compared with the core oligosaccharides in the cell walls of other Gram-negative bacteria (containing a unique α-Kdo-(2→5)-[α-Kdo-(2→4)]-α-Kdo branched trisaccharide skeleton). Therefore, the core hexasaccharide (“core hexasaccharide”) in the lipopolysaccharide of Acinetobacter baumannii ATCC 17904 serum type is selected (see Appendix). Figure 1Using compounds 7, 9, 8a, and 8b as Kdo monosaccharide building blocks and orthogonally substituted α-Kdo-(2→5)-Kdo disaccharides 5 and 6 as key precursors, a flexible and divergent method was established to synthesize the target sugar. Protecting groups at different positions in these disaccharide precursors were selectively removed, followed by α-stereocontrolled coupling reactions with 5,7-O-di-tert-butylsiliconyl or 5-O-benzoyl-protected Kdo thioglycosides and 2-azido-2-deoxyglucosyl thioglycosides to elongate the sugar chains. This enabled efficient assembly of the target molecule, ultimately synthesizing four oligosaccharide fragments (compounds 1-4) of varying lengths and structures (e.g., branched or linear). All four oligosaccharide fragments possess antigenicity, and the branched trisaccharides included in their structures are common to the core oligosaccharides within the cell walls of different serotypes of Acinetobacter baumannii. Therefore, these four oligosaccharide fragments can be used to prepare immunoassay reagents to detect the presence of corresponding antibodies in test samples, i.e., to determine the presence of infection caused by Acinetobacter baumannii. Furthermore, these four oligosaccharide fragments can be conjugated with suitable proteins to form glycoconjugates, which can then be used to prepare vaccines for the treatment or prevention of diseases caused by Acinetobacter baumannii.

[0043] It is worth noting that although the technical solution of this invention aims to synthesize four oligosaccharide fragments of different lengths and structures of the core hexasaccharide, rather than following the conventional approach of synthesizing or obtaining the core hexasaccharide as the final goal, this is to better balance the contradiction between the pursuit of antigenicity and the complexity and ease of the synthesis method. The technical solution of this invention considers that direct chemical synthesis of the core hexasaccharide would make the synthesis method and process more complex and difficult to apply in practice, while the method of purifying the core hexasaccharide by culturing Acinetobacter baumannii through biological means is difficult to guarantee the efficiency, purity, and quality of the purified product. Attached Figure Description

[0044] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the accompanying drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without any creative effort.

[0045] Figure 1 The core oligosaccharide of serum-type lipopolysaccharide from Acinetobacter baumannii ATCC 17904 is shown;

[0046] Figure 2a Four oligosaccharide molecules synthesized in this invention are shown;

[0047] Figure 2bThe invention illustrates the Kdo key disaccharides 5 and 6 and the Kdo monosaccharide building blocks, including compounds 7, 9, 8a, and 8b.

[0048] Figure 3 The synthetic route of compounds in Example 2 of the present invention is shown, including compounds 5, 12, 10 and 11;

[0049] Figure 4 The synthetic route of compounds in Synthetic Example 6 is shown, including compounds 25, 26, 27, 28 and 4;

[0050] Figure 5 The synthetic route of compounds in Synthetic Example 3 is shown, including compounds 13, 14, 1, 15, 16 and 2;

[0051] Figure 6 The synthetic route of compounds in Synthetic Example 5 is shown, including compounds 6, 17, 18, 19, 20, 22, 23, 24 and 3;

[0052] Figure 7 The synthetic routes for intermediate compounds S-1 to S-2 and 9 of Synthetic Example 1 are shown;

[0053] Figure 8 The synthetic routes for intermediate compounds S-3 to S-8 and 21 of synthetic Example 4 are shown;

[0054] Figure 9 The synthetic routes for intermediate compounds S-9 to S-19 are shown;

[0055] Figure 10 The synthetic routes for intermediate compounds S-19 to S-24 and 29 are shown.

[0056] Figure 11 The results of human serum screening of the glycochip are shown: (a) Glycochip spotting patterns; 1: trisaccharide; 2: tetrasaccharide; 3: tetrasaccharide; 4: trisaccharide; 29: tetrasaccharide, with spotting concentrations of 2 mM and 10 mM, respectively; (b) Cy3 fluorescence scan of the chip; (c) Quantitative average fluorescence intensity of the chip scan. The error bar represents the standard deviation of fluorescence intensity from two spots at the same concentration.

[0057] Figures 12a-12e The structural identification spectrum of compound 1: 12a is 1 H NMR; 12b is 13 C NMR; 12c is gCOSY; 12d is gHMQC; 12e is gHMBC;

[0058] Figures 13a-13e Structural identification spectrum of compound 2: 13a is 1 H NMR; 13b is 13 C NMR; 13c is gCOSY; 13d is gHMQC; 13e is gHMBC;

[0059] Figures 14a-14e Structural identification spectrum of compound 3: 14a is 1 H NMR; 14b is 13 C NMR; 14c is gCOSY; 14d is gHMQC; 14e is gHMBC;

[0060] Figures 15a-15e Structural identification spectrum of compound 4: 15a is 1 H NMR; 15b is 13 C NMR; 15c is gCOSY; 15d is gHMQC; 15e is gHMBC. Detailed Implementation

[0061] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0062] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.

[0063] As used in this specification, the term "about" typically means + / - 5% of the value, more typically + / - 4%, more typically + / - 3%, more typically + / - 2%, even more typically + / - 1%, even more typically + / - 0.5% of the value.

[0064] In this specification, certain embodiments may be disclosed in a range-bound format. It should be understood that this "range-bound" description is merely for convenience and brevity and should not be construed as a rigid limitation on the disclosed range. Therefore, the description of the range should be considered as having specifically disclosed all possible subranges and independent numerical values ​​within those ranges. For example, range The description should be considered as having specifically disclosed subranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as individual numbers within this range, such as 1, 2, 3, 4, 5, and 6. The above rules apply regardless of the breadth of the range.

[0065] In this invention, the structure shown in formula (1) is α-Kdo-(2→5)-[α-Kdo-(2→4)]-α-Kdo branched trisaccharide 1, i.e., compound 1; the structure shown in formula (2) is α-Kdo-(2→5)-α-Kdo-(2→5)-[α-Kdo-(2→4)]-α-Kdo branched tetrasaccharide 2, i.e., compound 2; the structure shown in formula (3) is α-GlcNA-(1→4)-α-Kdo-(2→5)-[α-Kdo-(2→4)]-α-Kdo branched tetrasaccharide 3, i.e., compound 3; and the structure shown in formula (4) is α-Kdo-(2→5)-α-Kdo-(2→5)-α-Kdo linear trisaccharide 4, i.e., compound 4.

[0066] Example 1

[0067] Chip detection of oligosaccharide synthesis by Acinetobacter baumannii

[0068] The antigenicity of branched-chain Kdo oligosaccharides was elucidated by screening patient serum using a polysaccharide microarray.

[0069] Experimental Methods: Samples were spotted onto NHS slides (Sur Modics, DN01-0025) using a chip spotting instrument. After spotting, the slides were incubated overnight at 26°C and 55% humidity. The slides were then immersed in solution B (50 nM Na₂HPO₄, 100 nM ethanolamine aqueous solution) at 50°C for 1 hour. The slides were washed three times with ultrapure water and centrifuged to dryness. The slides were then blocked overnight at 4°C using 3% BSA (w / v) PBS solution. The slides were washed once with PBST (PBS containing 0.1% Tween) and twice with PBS, and centrifuged to dryness. The slides were then placed into 16-well incubators (ProPlate). 120 μL of human serum sample diluted 1:50 with 1% BSA (w / v) PBS solution was added to each well, and the incubator was humidified at 37°C in the dark for 1 hour. Remove the samples, wash three times with PBST, add secondary antibody diluted 1:400 in PBS solution with 1% BSA (w / v), and incubate in a humidified chamber at 37°C in the dark for 45 minutes. Remove the secondary antibody solution and wash three times with PBST. Wash again with ultrapure water, centrifuge, and scan using a microarray scanner. The human serum samples were from 11 different patients (P1–P11).

[0070] Experimental Results: After screening, compound 1 was recognized by IgG antibodies in most serum samples, indicating that it may be the main structure with high antigenicity. Compound 1 showed lower binding affinity to serum IgG antibodies compared to compound 2, which has a Kdo residue at the 5”-branch site, indicating that adding the Kdo residue did not improve antigenicity. Compound 3, with a GlcpNA residue at the 4”-branch site of compound 1, also exhibited antigenicity, but its affinity for IgG was weaker compared to other compounds, suggesting that the GlcpNA residue may not be conducive to IgG binding. Compound 4 showed strong IgG binding affinity in some patient samples, indicating that this structure may exhibit superior antigenicity in certain serotypes and therefore could be used to prepare immunoassay reagents or vaccines targeting specific serotypes.

[0071] In summary, this experiment used patient serum to assess the antigenicity of the synthesized core oligosaccharide fragments 1-4. The results indicate that 4,5-branched Kdo trisaccharide 1 possesses good antigenicity and can be used for further immunological research and vaccine design, such as... Figure 11 The results of screening the sugar chip using human serum are shown.

[0072] The following synthetic examples illustrate the synthetic routes and methods for the four oligosaccharide molecules and key intermediates described in this invention.

[0073] Synthesis Example 1

[0074] Synthesis of compound S-2

[0075] Compound S-1[1] (1.05 g, 1.77 mmol) was dissolved in tetrahydrofuran (17.7 mL), and TBAF (3.5 mL, 3.5 mmol, 1 mol / L in THF) was added. The reaction was carried out at room temperature for 3 hours. After the reaction was complete, the solution was concentrated under reduced pressure. The crude product obtained after concentration was dissolved in dichloromethane / anhydrous methanol (1:1, v / v, 18 mL), and sodium methoxide (96 mg, 1.77 mmol) was added under ice bath conditions. The reaction system was brought to room temperature and the reaction was carried out for 2 hours. After the reaction was complete, the solution was analyzed using Amberlite IR 120 H. + The pH was adjusted to neutral using a cation exchange resin. The mixture was filtered, and the filtrate was concentrated under reduced pressure. The crude product obtained after concentration was purified by silica gel column chromatography (2:1, petroleum ether-ethyl acetate) to give a colorless syrupy compound S-2 (564 mg, 85% after two steps). Structural identification of compound S-2: R f =0.27 (1:1, petroleum ether-ethyl acetate); 1 H NMR(400MHz, CDCl3) δ4.45–4.36(m,1H),4.18(dd,J=8.8,6.1Hz,1H),4.11–4.02(m,2H),3.98(dd,J=8.8,4.6Hz,1H),3.79 (s,3H),3.57–3.48(m,2H),3.46–3.35(m,3H),2.16(dd,J=12.6,5.3Hz,1H),1.93–1.77(m,3H),1.43(s,3H),1.38(s,3H); 13 C NMR (100MHz, CDCl3) δ168.7,109.7,99.3,73.7,73.2,67.3,66.8,65.9,60.5,52.9,48.3,35.1,28.9,27.0,25.4; HRMS (ESI): m / z calcd for C 15 H 25 N3O8[M+Na] + :398.1540,found:398.1537.

[0076] Synthesis of Compound 9

[0077] Compound S-2 (651 mg, 1.74 mmol) was dissolved in dry methanol (34.7 mL), and dibutyltin oxide (648 mg, 2.60 mmol) was added. The mixture was heated to 90 °C and refluxed for 3 hours. After the reaction system cooled to room temperature, it was concentrated under reduced pressure. The concentrated product was dissolved in dry DMF (17.4 mL), and bromopropylene (0.19 mL, 2.26 mmol) and cesium fluoride (527 mg, 3.47 mmol) were added. The mixture was reacted at 40 °C for 8 hours. After the reaction was complete, the mixture was diluted with dichloromethane, and the reaction was terminated with saturated ammonium chloride aqueous solution. The organic phase was then washed with water, washed with saturated brine, dried over anhydrous sodium sulfate, filtered, concentrated under reduced pressure, and the crude product was purified by silica gel column chromatography (2:1, petroleum ether-ethyl acetate) to give a white solid compound 9 (627 mg, 87% after two steps). The structure of compound 9 was identified as R. f =0.49 (3:2, petroleum ether-ethyl acetate); 1 H NMR (400MHz, CDCl3) δ5.98–5.82(m,1H),5.34–5.24(m,1H),5.23–5.17(m,1H),4.50–4. 42(m,1H),4.16(dd,J=8.8,6.2Hz,1H),4.13–4.06(m,3H),4.00(dd,J=8.8,4.9Hz,1H),3 .86–3.79(m,1H),3.78(s,3H),3.58–3.48(m,2H),3.47–3.35(m,3H),2.23(s,1H),2.15( dd,J=12.9,4.6Hz,1H),2.00–1.91(m,1H),1.91–1.78(m,2H),1.43(s,3H),1.38(s,3H); 13 C NMR (100MHz, CDCl3) δ168.6,134.4,117.6,109.5,99.2,73.7,73.0,72.7,69. 4,67.2,64.2,60.5,52.8,48.4,32.3,28.9,26.9,25.5; HRMS(ESI):m / zcalcd for C 18 H 29 N3O8[M+Na]+:438.1853,found:438.1856.

[0078] Synthesis Example 2

[0079] Synthesis of Compound 5

[0080] Kdo donor 7 [2](236 mg, 0.36 mmol) and receptor 9 (100 mg, 0.24 mmol) were dissolved in dry acetonitrile (8.0 mL), and activated [the drug] was added. After molecular sieve removal, the mixture was stirred at room temperature for 15 minutes. The reaction system was then placed in an ice bath and stirred for another 15 minutes. TBPA (353 mg, 0.42 mmol) was added in ten portions while maintaining the ice bath throughout the reaction, and the mixture was reacted in the dark for 5 hours. After the reaction was complete, the reaction was quenched with triethylamine. The mixture was diluted with dichloromethane, and the molecular sieve was removed by vacuum filtration. The filtrate was concentrated under reduced pressure, and the crude product was purified by silica gel column chromatography (5:1, petroleum ether-ethyl acetate) to give a colorless syrupy compound 5 (194 mg, 80%). Structure identification of compound 5: R f =0.50 (3:1, petroleum ether-ethyl acetate); 1 H NMR (400MHz, CDCl3) δ8.10–8.01(m,2H),7.60–7.52(m,1H),7.48–7.40(m, 2H),5.92–5.77(m,1H),5.59–5.49(m,1H),5.27–5.12(m,2H),4.55(d,J=2 .6Hz,1H),4.44–4.34(m,2H),4.28(s,1H),4.20–4.12(m,2H),4.12–4.05( m,1H),4.01–3.96(m,1H),3.93(dd,J=8.6,4.9Hz,1H),3.84–3.73(m,5H), 3.71(s,3H),3.70–3.65(m,1H),3.55–3.47(m,2H),3.47–3.42(m,1H),3.4 2–3.33(m,2H),2.83(t,J=12.9Hz,1H),2.57(dd,J=13.4,4.4Hz,1H),2.28 (t,J=12.3Hz,1H),2.12–2.03(m,1H),1.89–1.76(m,2H),1.42(s,3H),1.3 7(s,3H),1.03(s,9H),0.95(s,9H),0.89(s,9H),0.07(s,3H),0.06(s,3H); 13C NMR (100MHz, CDCl3) δ168.5,168.0,165.8,134.8,132.9,130.8,129.7,128.5,117.3,109.7,100.4,99.3,77.1,74.5,73.9,72.9,71.5,70.0,69 .7,69.2,67.7,67.1,66.6,60.4,52.7,52.4,48.4,32.6,29.0,28.5,27 .6,27.3,27.0,26.2,25.5,22.3,21.6,18.7,-5.2,-5.3; HRMS(ESI):m / z calcd for C 48 H 77 N3O 16 Si2[M+Na] + :1030.4740,found:1030.4730.

[0081] Synthesis of Compounds 10 and 11

[0082] Iridium complex ([Ir(COD)(PMePh2)2]PF6, 28 mg, 34 μmol) was dissolved in dry tetrahydrofuran (1.5 mL) and stirred at room temperature under hydrogen atmosphere for 30 minutes until the color changed from red to colorless to pale yellow. After exchanging the hydrogen with argon, 5 (170 mg, 0.17 mmol) dissolved in 1.5 mL THF solution was added, and the reaction was allowed to proceed for 1 hour. After the reaction was complete, the solvent was dried under vacuum. The crude product was dissolved in acetone / H2O (3 mL, 4:1; v / v), and then mercuric chloride (54 mg, 0.24 mmol) and mercuric oxide (51 mg, 0.20 mmol) were added. The mixture was stirred at room temperature for 6 hours and then filtered through diatomaceous earth. The filtrate was concentrated under reduced pressure, diluted with ethyl acetate, and washed successively with 10% KI solution, water, and saturated brine. The organic layer was dried over anhydrous sodium sulfate, filtered, and concentrated under reduced pressure. The concentrated crude product was purified by silica gel column chromatography (5:1, petroleum ether-ethyl acetate) to give colorless syrupy compounds 10 (122 mg, 75%) and 11 (21 mg, 13%). Structure identification of compound 10: R f =0.34 (3:1, petroleum ether-ethyl acetate); 1H NMR (400MHz, CDCl3) δ8.10–7.99(m,2H),7.63–7.50(m,1H),7.44(t,J=7.6Hz,2H),5.40–5.32(m,1H),4.66(d,J= 2.4Hz,1H),4.39–4.30(m,1H),4.26(s,1H),4.20–4.12(m,2H),4.11–3.99(m,3H),3.80(s,6H),3.78–3.73(m,2H ),3.60–3.48(m,2H),3.48–3.30(m,4H),2.65–2.50(m,2H),2.13(dd,J=12.4,4.4Hz,1H),1.90(t,J=12.4Hz,1H) ,1.86–1.76(m,2H),1.39(s,3H),1.35(s,3H),1.03(s,9H),0.94(s,9H),0.89(s,9H),0.07(s,3H),0.06(s,3H); 13 C NMR (100MHz, CDCl3) δ168.4,166.9,165.8,133.1,130.5,129.7,128.5,109.2,100.2,99.2,77.0,74.2,73.6,73.6,72.5,69.5,67.1, 66.9,66.7,66.1,60.5,52.8,52.8,48.4,36.0,31.9,29.0,27.7,27.3,27.0,26.2,25.6,22.2,21.7,18.6,-5.2,-5.3; HRMS(ESI):m / z calcd forC 45 H 73 N3O 16 Si2[M+Na] + :990.4427, found:990.4421. Structure identification of compound 11: R f =0.43 (2.5:1, petroleum ether-ethyl acetate); 1H NMR (400MHz, CDCl3) δ8.07–8.01(m,2H),7.59–7.52(m,1H),7.48–7.39(m,2H),5.40–5.31(m,1H),4.88–4.77(m,1H),4.63(d,J=2.6Hz ,1H),4.46–4.38(m,1H),4.38–4.33(m,2H),4.16(dd,J=8.8,6.2Hz,1H),4.09(dd,J=7.0,4.7Hz,1H),3.99(dd,J=8.8,4.8Hz,1H),3.78 (s,3H),3.77–3.73(m,1H),3.71–3.62(m,2H),3.58–3.50(m,1H),3.48–3.35(m,3H),2.80(t,J=12.4Hz,1H),2.48(dd,J=12.8,4.4Hz, 1H),2.43–2.28(m,2H),1.89–1.76(m,2H),1.41(s,3H),1.38(s,3H),1.11(s,9H),0.93(s,9H),0.89(s,9H),0.09(s,3H),0.08(s,3H); 13 C NMR (100MHz, CDCl3) δ167.2,165.7,163.7,133.1,130.4,129.7,128.5,109.8,98.8,98.2,76.7,73.6,72.9,72.0,71.6,69.3,67. 2,66.4,65.6,64.6,60.6,52.7,48.1,34.0,29.0,28.7,27.6,27.2,26.8,25.9,25.0,22.2,21.7,18.3,-5.2,-5.4; HRMS(ESI):m / z calcd for C 44 H 69 N3O 15 Si2[M+Na] + :958.4165,found:958.4155.

[0083] Synthesis of Compound 12

[0084] Compound 5 (500 mg, 0.50 mmol) was dissolved in dry tetrahydrofuran (5 mL), and triethylamine trihydrofluoric acid (0.5 mL) was added under ice bath conditions. The reaction mixture was brought to room temperature and reacted for 8 hours. After the reaction was complete, the mixture was concentrated under reduced pressure. The crude product obtained after concentration was purified by silica gel column chromatography (40:1, dichloromethane-methanol) to obtain a colorless syrup-like compound. The obtained compound was dissolved in DMF (4.3 mL), and 2,2-dimethoxypropane (79 μL, 0.65 mmol) and p-toluenesulfonic acid (8 mg, 0.043 mmol) were added at 0 °C. The reaction mixture was brought to room temperature and reacted for 3 hours. After the reaction was complete, the reaction was quenched with triethylamine, concentrated under reduced pressure, and the crude product obtained after concentration was purified by silica gel column chromatography (3:1, petroleum ether-ethyl acetate) to obtain a colorless syrup-like compound 12 (288 mg, 73%). The structure of compound 12 was identified as R. f =0.51 (1:1, petroleum ether-ethyl acetate); 1 H NMR (400MHz, CDCl3) δ8.10–8.02(m,2H),7.63–7.54(m,1H),7.50–7.42(m,2H), 5.89–5.76(m,1H),5.73–5.64(m,1H),5.26–5.18(m,1H),5.18–5.12(m,1H),4. 48(s,1H),4.47–4.36(m,2H),4.33–4.28(m,1H),4.20(dd,J=8.8,6.1Hz,1H),4 .11(dd,J=8.7,6.4Hz,1H),4.06(dd,J=7.6,1.1Hz,1H),4.04–4.01(m,1H),4.0 1–3.93(m,3H),3.89–3.83(m,1H),3.81(s,3H),3.70(s,3H),3.58(dd,J=9.1,1 .5Hz,1H),3.55–3.47(m,1H),3.44–3.32(m,3H),2.83(d,J=14.0Hz,1H),2.67( dd,J=14.0,4.6Hz,1H),2.52(d,J=3.6Hz,1H),2.26(t,J=12.2Hz,1H),2.13(dd ,J=12.6,4.2Hz,1H),1.90–1.75(m,2H),1.45(s,3H),1.41(s,3H),1.35(s,6H); 13C NMR (100MHz, CDCl3) δ168.4,168.1,165.7,134.6,133.3,130.1,129.8,128.6,117.5,109.9,109.7,100.7,99.2,74.3,74.1,73.8 ,73.1,72.9,70.0,69.7,69.5,67.9,67.6,65.4,60.4,52.8,52.5,48.4,31.7,28.9,27.3,27.1,26.9,25.5,25.2; HRMS(ESI):m / z calcd forC 37 H 51 N3O 16 [M+Na] + :816.3167,found:816.3167.

[0085] Synthesis Example 3

[0086] Synthesis of Compound 13

[0087] Kdo donor 8a [1] (98 mg, 0.18 mmol) and receptor 10 (60 mg, 0.062 mmol) were dissolved in dry acetonitrile (2.1 mL), and activated [the drug / method] was added. After molecular sieve removal, the mixture was stirred at room temperature for 15 minutes. The reaction system was then placed in an ice bath and stirred for another 15 minutes. TBPA (181 mg, 0.22 mmol) was added in ten portions while maintaining the ice bath throughout the reaction, and the mixture was reacted in the dark for 10 hours. After the reaction was complete, the reaction was quenched with triethylamine. The mixture was diluted with dichloromethane, and the molecular sieve was removed by vacuum filtration. The filtrate was concentrated under reduced pressure, and the crude product was purified by silica gel column chromatography (6:1, petroleum ether-ethyl acetate) to give a colorless syrupy compound 13 (62 mg, 70%). Structure identification of compound 13: R f Not equal to 0.50 (4:1, toluene-ethyl acetate); 1H NMR(600MHz,CDCl3)δ8.14–8.08(m,2H),8.08–8.03(m,2H),7.61–7.53(m,2H),7.51–7.40(m,4H),7.37–7.32(m,2H),7.30–7.26(m,2H),7.24–7.19(m,1H),5.86–5.77(m,2H),4.91(d,J=11.4Hz,1H),4.62–4.54(m,2H),4.49–4.42(m,1H),4.37(s,1H),4.31–4.25(m,2H),4.21–4.14(m,4H),4.00–3.91(m,3H),3.87(d,J=5.9Hz,1H),3.80–3.72(m,7H),3.69–3.63(m,1H),3.60(s,1H),3.58(s,3H),3.55–3.49(m,1H),3.47–3.36(m,3H),3.13(t,J=13.6Hz,1H),2.72(dd,J=14.4,4.5Hz,1H),2.52(t,J=12.4Hz,1H),2.34(dd,J=13.4,5.1Hz,1H),2.20(dd,J=12.3,4.2Hz,1H),2.05(t,J=12.5Hz,1H),1.87–1.77(m,2H),1.49(s,3H),1.44(s,6H),1.32(s,3H),1.05(s,9H),0.93(s,9H),0.92(s,9H),0.10(s,6H); 13 C NMR(150MHz,CDCl3)δ168.4,168.3,167.9,165.6,165.4,138.3,133.3,133.0,130.7,130.0,130.0,129.7,128.6,128.5,128.4,127.9,127.6,110.2,109.5,101.0,100.9,99.2,77.0,74.9,74.3,72.7,72.6,72.1,72.0,71.3,70.6,70.0,68.9,68.1,66.4,65.9,65.8,65.8,60.2,52.8,52.5,52.0,48.2,33.5,33.3,28.7,27.6,27.2,27.0,26.6,26.3,25.8,25.4,24.8,22.2,21.6,18.8,-5.0,-5.3;HRMS(ESI):m / zcalcd for C 71 H 101 N3O24 Si2[M+Na] + :1458.6212,found:1458.6212.

[0088] Synthesis of Compound 14

[0089] Compound 13 (261 mg, 0.18 mmol) was dissolved in dry tetrahydrofuran (3.6 mL), and triethylamine trihydrofluoric acid (0.36 mL) was added under ice bath conditions. The reaction mixture was brought to room temperature and reacted for 6 hours. After the reaction was complete, the mixture was concentrated under reduced pressure. The crude product obtained after concentration was purified by silica gel column chromatography (40:1, dichloromethane-methanol) to give a colorless syrupy compound 14 (187 mg, 87%). The structure of compound 14 was identified as: R f =0.25 (15:1, dichloromethane-methanol); 1 H NMR (400MHz, CDCl3) δ8.16–8.07(m,2H),8.07–8.02(m,2H),7.61–7.53(m,2H),7.49–7.40(m,4H),7.33–7.15(m,5H),5.93–5.84(m,1H) ,5.77(s,1H),4.87(d,J=11.4Hz,1H),4.56(d,J=11.4Hz,1H),4.53–4.46(m,2H),4.41–4.35(m,1H),4.26–4.12(m,5H),3.97–3.84(m,6H ),3.82(s,3H),3.75(s,3H),3.72–3.66(m,1H),3.65(s,3H),3.63–3.58(m,1H),3.53–3.45(m,1H),3.44–3.33(m,3H),3.03–2.95(m,2H ),2.88–2.78(m,2H),2.37–2.19(m,4H),2.05(t,J=12.5Hz,1H),1.82–1.77(m,2H),1.51(s,3H),1.43(s,3H),1.42(s,3H),1.32(s,3H); 13C NMR (150MHz, CDCl3) δ168.6,168.4,168.3,165.4,165.4,138.1,133.4,133.4,130.1,130 .0,129.8,128.7,128.6,128.4,127.9,127.7,110.4,109.4,101.4,101.1,99.4,74.9,74 .8,72.4,72.4,71.9,71.9,71.7,71.1,70.7,70.6,68.8,68.0,65.9,65.5,65.5,62.1,60 .6,53.1,53.0,52.6,48.1,33.6,33.6,29.8,28.6,26.8,26.5,25.9,25.3; HRMS(ESI):m / z calcd for C 57 H 71 N3O 24 [M+Na] + :1204.4326,found:1204.4325.

[0090] Synthesis of Compound 1

[0091] Compound 14 (25 mg, 0.021 mmol) was dissolved in dichloromethane (2.5 mL), and TFA / H2O (9:1, v / v, 0.25 mL) was added at 0 °C. The reaction mixture was brought to room temperature and reacted for 30 minutes. After the reaction was complete, dichloromethane was added to dilute the mixture, and the reaction was terminated with saturated sodium bicarbonate solution. The organic phase was then washed with water, saturated brine, dried over anhydrous sodium sulfate, filtered, and concentrated under reduced pressure. The crude product obtained after concentration was purified by silica gel column chromatography (30:1, dichloromethane-methanol) to give a colorless syrupy compound. The obtained compound was dissolved in CH3OH / H2O (v / v, 2:1, 3.0 mL), and 1 mol / L NaOH aqueous solution (1.0 mL) was added under ice bath conditions. The reaction mixture was brought to room temperature and reacted for 12 hours. After the reaction was complete, the mixture was analyzed using an Amberlite IR120 H2O filter. + The pH was adjusted to 8 using a cation exchange resin. The mixture was filtered, and the filtrate was dried under reduced pressure. The crude product was dissolved in t-BuOH / H2O (2:1, v / v, 3.0 mL), and Pd(OH)2 / C (20 mg) was added. The mixture was reacted in a hydrogen atmosphere for 8 hours. After the reaction was complete, the mixture was filtered, and the filtrate was freeze-dried. The crude product was then purified by size exclusion chromatography (BioGel P-2; eluent: 0.05 M NH4HCO3). The fraction containing the product was freeze-dried to give a white, foamy product 1 (9 mg, 58%). Structure identification of compound 1: R f=0.27(10:3,MeOH-H2O); 1 H NMR(400MHz,D2O)δ4.44–4.33(m,2H),4.21(d,J=8.8Hz,1H),4.17–4.09(m,1H),4.09–4.01(m,3H),4.01–3.9 1(m,4H),3.91–3.83(m,2H),3.81(dd,J=12.2,5.0Hz,1H),3.71(d,J=7.5Hz,1H),3.69–3.64(m,1H),3.64–3. 56(m,3H),3.37–3.28(m,1H),3.21–3.12(m,1H),3.09–2.98(m,1H),2.72(dd,J=13.9,4.9Hz,1H),2.34(t,J= 12.2Hz,1H),2.24(t,J=13.1Hz,1H),2.13(dd,J=13.0,4.9Hz,1H),2.04–1.83(m,3H),1.78(t,J=12.6Hz,1H); 13 CNMR(150MHz,D2O)δ175.9,175.6,174.9,102.6,101.0,100.6,72.8,72.6,72.1,71.3,70.7,69.6,68 .9,68.9,66.6,66.5,65.6,65.4,63.2,63.2,62.5,61.9,38.8,34.7,34.3,31.2,26.8; HRMS(ESI):m / z calcd for C 27 H 45 NO 22 [MH] - :734.2355,found:734.2354.

[0092] In summary, the synthesis steps of compound 1 are as follows: 1) Using compounds 9 and 7 as starting materials, compound 5 is obtained by glycosylation reaction; 2) Compound 5 is obtained by deallylation reaction; 3) Compound 10 and compound 8a are obtained by glycosylation reaction; 4) Compound 13 is obtained by desilication reaction; 5) Compound 14 is obtained by deisopropylidene ketalization reaction, saponification reaction and catalytic hydrogenation reduction reaction.

[0093] Synthesis of Compound 15

[0094] Compound 14 (63 mg, 0.053 mmol) was dissolved in DMF (0.5 mL), and 2,2-dimethoxypropane (9.8 μL, 0.080 mmol) and p-toluenesulfonic acid (1 mg, 0.005 mmol) were added at 0 °C. The reaction mixture was brought to room temperature and reacted for 2 hours. After the reaction was complete, the reaction was quenched with triethylamine, concentrated under reduced pressure, and the crude product was purified by silica gel column chromatography (3:1, petroleum ether-ethyl acetate) to give a colorless syrupy compound 15 (56 mg, 86%). The structure of compound 15 was identified as: R f =0.33 (1:1, petroleum ether-ethyl acetate); 1 H NMR(600MHz, CDCl3)δ8.13–8.06(m,2H),8.06–8.01(m,2H),7.61–7.51(m,2H),7 .50–7.37(m,4H),7.36–7.29(m,2H),7.29–7.23(m,2H),7.23–7.17(m,1H),5.94 –5.84(m,1H),5.77(s,1H),4.87(d,J=11.1Hz,1H),4.57(d,J=11.2Hz,1H),4.50 –4.40(m,2H),4.40–4.29(m,2H),4.26–4.14(m,4H),4.13–4.01(m,3H),4.01–3. 93(m,2H),3.93–3.86(m,2H),3.79(s,3H),3.72(s,3H),3.63(s,3H),3.62–3.59 (m,1H),3.56–3.48(m,1H),3.46–3.34(m,3H),2.98(t,J=13.4Hz,1H),2.87–2.7 9(m,1H),2.41(t,J=11.7Hz,1H),2.31–2.23(m,2H),2.03(t,J=12.0Hz,1H),1.8 6–1.79(m,2H),1.51(s,3H),1.43(s,3H),1.41(s,6H),1.35(s,3H),1.32(s,3H); 13CNMR (150MHz, CDCl3) δ168.6,168.5,168.0,165.4,165.3,138.2,133.4,130.1,130.0,129.9, 129.8,128.7,128.6,128.4,127.9,127.6,110.3,109.7,109.4,101.4,100.9,99.2,74.7,74.5 ,73.5,73.3,72.9,72.4,72.4,72.0,70.7,70.2,68.7,67.9,67.7,66.0,65.6,65.1,60.2,52. 9,52.6,52.3,48.2,33.6,33.2,29.8,28.7,27.1,27.0,26.5,25.9,25.5,25.3; HRMS(ESI):m / z calcd for C 60 H 75 N3O 24 [M+Na] + :1244.4639,found:1244.4638.

[0095] Synthesis of Compound 16

[0096] Kdo donor 7 (100 mg, 0.15 mmol) and acceptor 15 (62 mg, 0.05 mmol) were dissolved in dry acetonitrile (1.7 mL), and activated [the solution] was added. After molecular sieve removal, the mixture was stirred at room temperature for 15 minutes. The reaction system was then placed in an ice bath and stirred for another 15 minutes. TBPA (150 mg, 0.18 mmol) was added in ten portions while maintaining the ice bath throughout the reaction, and the mixture was reacted in the dark for 10 hours. After the reaction was complete, the reaction was quenched with triethylamine. The mixture was diluted with dichloromethane, and the molecular sieve was removed by vacuum filtration. The filtrate was concentrated under reduced pressure, and the crude product was purified by silica gel column chromatography (2:1, petroleum ether-ethyl acetate) to give a colorless syrupy compound 16 (46 mg, 50%). Structure identification of compound 16: R f =0.22 (2:1, petroleum ether-ethyl acetate); 1H NMR(600MHz,CDCl3)δ8.16–8.08(m,2H),8.08–7.98(m,4H),7.62–7.51(m,3H),7.50–7.39(m,6H),7.34–7.30(m,2H),7.26–7.23(m,2H),7.19(t,J=7.3Hz,1H),5.80(s,1H),5.80–5.73(m,1H),5.62–5.55(m,1H),4.90(d,J=11.3Hz,1H),4.57(d,J=11.2Hz,1H),4.56–4.53(m,2H),4.52–4.43(m,2H),4.37–4.33(m,1H),4.27–4.21(m,2H),4.21–4.14(m,3H),4.13–4.07(m,3H),4.05(t,J=5.9Hz,1H),4.02–3.96(m,2H),3.94–3.88(m,2H),3.80(s,3H),3.74(s,3H),3.67(s,3H),3.66(s,3H),3.63–3.49(m,4H),3.47–3.35(m,3H),3.11(t,J=13.4Hz,1H),2.83–2.74(m,2H),2.44(dd,J=13.0,4.8Hz,1H),2.39(t,J=12.1Hz,1H),2.31(dd,J=13.2,4.9Hz,1H),2.23(dd,J=12.4,4.6Hz,1H),2.09(t,J=12.4Hz,1H),1.86–1.79(m,2H),1.45(s,3H),1.44(s,3H),1.41(s,6H),1.37(s,3H),1.32(s,3H),1.01(s,9H),0.92(s,9H),0.82(s,9H),0.01(s,3H),-0.00(s,3H); 13C NMR (150MHz, CDCl3) δ168.6,168.2,168.0,167.6,166.5,165.7,165.4,138.2,133.3,133.2,132.9,130.7,130.4,130.1,130.0,13 0.0,129.7,128.6,128.4,128.4,128.3,127.8,127.5,110.2,109.6,109.5,101.2,100.9,100.6,99.2,76.9,74.9,74.7,74.5,72. 9,72.7,72.6,72.0,72.0,71.3,70.6,70.6,70.2,70.1,69.6,68.2,67.9,66.6,66.1,65.9,65.7,60.3,52.9,52.6,52.2,52.1,48. 2,33.7,33.4,29.0,28.7,27.7,27.2,27.1,27.0,26.9,26.5,26.1,25.9,25.4,25.3,22.1,21.6,18.5,-5.1,-5.3; HRMS(ESI):m / z calcd forC 90 H 123 N3O 32 Si2[M+Na] + :1836.7526,found:1836.7521.

[0097] Synthesis of Compound 2

[0098] Compound 16 (17 mg, 0.0094 mmol) was dissolved in dry tetrahydrofuran (1.0 mL), and triethylamine trihydrofluoric acid (0.1 mL) was added under ice bath conditions. The reaction mixture was brought to room temperature and reacted for 6 hours. After the reaction was complete, the reaction mixture was concentrated under reduced pressure. The crude product obtained after concentration was purified by silica gel column chromatography (40:1, dichloromethane-methanol) to give a colorless syrupy compound. The obtained compound was dissolved in dichloromethane (1.6 mL), and TFA / H₂O (9:1, v / v, 0.16 mL) was added at 0 °C. The reaction mixture was brought to room temperature and reacted for 30 minutes. After the reaction was complete, the reaction mixture was diluted with dichloromethane, and the reaction was terminated with saturated sodium bicarbonate aqueous solution. The organic phase was then washed with water, washed with saturated brine, dried over anhydrous sodium sulfate, filtered, and concentrated under reduced pressure. The crude product was purified by silica gel column chromatography (20:1, dichloromethane-methanol) to give a colorless syrupy compound. The compound was dissolved in CH3OH / H2O (v / v, 2:1, 3.0 mL), and 1 mol / L NaOH aqueous solution (1.0 mL) was added under ice bath conditions. The reaction system was brought to room temperature and reacted for 12 hours. After the reaction was complete, the product was analyzed using an Amberlite IR120 H2O analyzer. + The pH was adjusted to 8 using a cation exchange resin. The mixture was filtered, and the filtrate was dried under reduced pressure. The crude product was dissolved in t-BuOH / H2O (2:1, v / v, 3.0 mL), and Pd(OH)2 / C (20 mg) was added. The mixture was reacted in a hydrogen atmosphere for 8 hours. After the reaction was complete, the mixture was filtered, and the filtrate was lyophilized. The crude product was then purified by size exclusion chromatography (BioGel P-2; eluent: 0.05 M NH4HCO3). The fraction containing the product was lyophilized to give a white, foamy product 2 (4 mg, 44% over four steps). Structure identification of compound 2: R f =0.25(4:1,MeOH-H2O); 1H NMR(400MHz,D2O)δ4.38–4.26(m,3H),4.20(d,J=9.3Hz,1H),4.15–4.06(m,4H),4.03–3.91(m, 7H),3.90–3.81(m,4H),3.81–3.76(m,1H),3.68(d,J=7.6Hz,1H),3.66–3.61(m,1H),3.61–3.5 3(m,3H),3.34–3.25(m,1H),3.20–3.10(m,1H),3.08–2.98(m,1H),2.65(dd,J=13.7,4.5Hz,1H ),2.39–2.23(m,3H),2.11(dd,J=13.2,4.9Hz,1H),2.02–1.83(m,4H),1.74(t,J=12.6Hz,1H); 13 C NMR(150MHz,D2O)δ175.9,175.4,174.9,174.0,102.8,102.1,101.0,100.6,73.6,73.2,72.6,72.1,72.0,72.0,70.8,70.7,69 .5,68.8,68.7,66.9,66.7,65.6,65.6,65.2,63.3,63.2,62.4,62.2,62.0,38.9,35.8,34.8,34.3,31.8,26.4; HRMS(ESI):m / z calcd for C 35 H 57 NO 29 [MH] - :954.2938,found:954.2937.

[0099] In summary, the synthesis steps of compound 2 are as follows: 1) Compound 5 is obtained by glycosylation of compound 9 and compound 7 as starting materials; 2) Compound 5 is obtained by deallylation of compound 5; 3) Compound 10 and compound 8a are obtained by glycosylation of compound 10 and compound 8a; 4) Compound 13 is obtained by desilication of compound 13 and compound 14; 5) Compound 14 is obtained by isopropyl ketal reaction of compound 14 and compound 15; 6) Compound 15 and compound 7 are obtained by glycosylation of compound 16 and compound 16; 7) Compound 16 is obtained by desilication, deisopropyl ketalization, saponification and catalytic hydrogenation reduction reaction.

[0100] Synthesis Example 4

[0101] Synthesis of compound S-4

[0102] Compound S-3 [3](37 g, 99.2 mmol) was dissolved in dry dichloromethane (200 mL), and thiophenol (25.3 mL, 248 mmol) and boron trifluoride ether (62.6 mL, 496 mmol) were added sequentially under ice bath conditions. The reaction mixture was brought to room temperature and reacted for 12 hours. After the reaction was complete, the reaction was quenched with triethylamine. The organic phase was diluted with dichloromethane, washed with water and saturated brine, and dried over anhydrous sodium sulfate. The mixture was concentrated under reduced pressure, and the crude product was purified by silica gel column chromatography (4:1, petroleum ether-ethyl acetate) to give a white solid compound S-4 (33.6 g, 80%, α:β = 2.5:1). Structural identification of compound S-4: R f =0.22 (4:1, petroleum ether-ethyl acetate); S-4α: 1 H NMR (400MHz, CDCl3) δ7.51–7.45(m,2H),7.37–7.27(m,3H),5.63(d,J=5.6Hz,1H),5.32(dd,J=10.6,9.1Hz,1H),5.10–4.99(m,1H),4.62–4. 55(m,1H),4.28(dd,J=12.4,5.1Hz,1H),4.07(dd,J=10.6,5.6Hz,1H),4.02(dd,J=12.3,2.2Hz,1H),2.07(s,3H),2.05(s,3H),1.99(s,3H); 13 C NMR (100MHz, CDCl3) δ170.5,169.9,169.9,134.2,132.3,129.3,128.2,86.6,72.1,68.8,68.6,62.0,61.7,20.7,20.7,20.7; S-4β: 1 H NMR (400MHz, CDCl3) δ7.60–7.55(m,2H),7.37–7.27(m,3H),5.10–4.99(m,1H),4.91(t,J=9.7Hz,1H),4.48(d,J=10.1Hz,1H),4.22(d d,J=12.3,4.9Hz,1H),4.16(dd,J=12.3,2.4Hz,1H),3.71–3.65(m,1H),3.39(t,J=9.9Hz,1H),2.09(s,3H),2.04(s,3H),2.01(s,3H); 13C NMR (100MHz, CDCl3) δ170.6,169.9,169.7,132.5,130.3,129.2,129.0,85.9,75.8,74.5,68.1,62.7,62.1,20.8,20.7,20.6.

[0103] Synthesis of compound S-5

[0104] Compound S-4 (2 g, 4.73 mmol) was dissolved in anhydrous methanol (30 mL), and sodium methoxide (153 mg, 2.84 mmol) was added under ice bath conditions. The reaction mixture was brought to room temperature and reacted for 2 hours. After the reaction was complete, the solution was analyzed using Amberlite IR120H. + The pH was adjusted to neutral using a cation exchange resin. The mixture was filtered, and the filtrate was concentrated under reduced pressure and purified by silica gel column chromatography (20:1, dichloromethane-methanol) to obtain a colorless syrupy compound. The obtained compound was dissolved in dry DMF (23.6 mL), and benzaldehyde dimethyl acetal (1.38 mL, 9.46 mmol) and a catalytic amount of camphor sulfonic acid (110 mg, 0.43 mmol) were added. The reaction system was heated to 60 °C and reacted for 1 hour. After the reaction was complete, the mixture was cooled to room temperature, quenched with triethylamine, concentrated under reduced pressure, and the crude product obtained after concentration was purified by silica gel column chromatography (5:1, petroleum ether-ethyl acetate) to give a white solid compound S-5 (1.18 g, 65%). Structural identification of compound S-5: R f =0.31 (4:1, petroleum ether-ethyl acetate); 1 H NMR (400MHz, CDCl3) δ7.56–7.47(m,4H),7.45–7.37(m,3H),7.36–7.29(m,3H),5.58(d,J=5.5Hz,1H),5.56(s,1H),4.44–4.36(m,1H),4.24(d d,J=10.4,5.0Hz,1H),4.12–4.05(m,1H),3.93(dd,J=10.0,5.6Hz,1H),3.76(t,J=10.3Hz,1H),3.59(t,J=9.3Hz,1H),2.77(d,J=2.4Hz,1H); 13 C NMR (100MHz, CDCl3) δ136.9,133.1,132.6,129.6,129.3,128.6,128.2,126.4,102.3,87.9,81.8,70.9,68.7,64.0,63.6; HRMS (ESI): m / z calcd for C 19 H 19N3O4S[M+Na] + :408.0994,found:408.0995.

[0105] Synthesis of compound S-6

[0106] Compound S-5 (1.25 g, 3.25 mmol) was dissolved in dry DMF (16.2 mL), and 60% NaH (519 mg, 13.0 mmol) and BnBr (2.31 mL, 19.5 mmol) were added sequentially under ice bath conditions. The reaction mixture was brought to room temperature and reacted for 1 hour. After the reaction was complete, it was quenched with a saturated ammonium chloride aqueous solution. The mixture was diluted with dichloromethane, washed with water and saturated brine, dried over anhydrous sodium sulfate, filtered, concentrated under reduced pressure, and the crude product was purified by silica gel column chromatography (8:1, petroleum ether-ethyl acetate) to give a white solid compound S-6 (1.34 g, 87%). Structural identification of compound S-6: R f =0.55 (4:1, petroleum ether-ethyl acetate); 1 H NMR (400MHz, CDCl3) δ7.55–7.46(m,4H),7.44–7.37(m,5H),7.37–7.27(m,6H),5.61(s,1H),5.57(dd,J=3.7,1.3Hz,1H),4.98(d ,J=10.9Hz,1H),4.84(d,J=10.9Hz,1H),4.48–4.39(m,1H),4.23(dd,J=10.4,5.0Hz,1H),4.02–3.93(m,2H),3.82–3.72(m,2H); 13 C NMR (100MHz, CDCl3) δ137.8,137.2,133.1,132.6,129.3,129.2,128.6,128.4,128 .4,128.1,126.1,101.6,88.0,82.8,78.0,75.3,68.7,63.9,63.7; HRMS(ESI):m / z calcd for C 26 H 25 N3O4S[M+Na] + :498.1464,found:498.1465.

[0107] Synthesis of compound S-7

[0108] S-6 (1.1 g, 0.027 mmol) was dissolved in dichloromethane (11.6 mL), and a small amount of H2O (0.5 mL) was added. TFA (0.69 mL) was added under ice bath conditions. The reaction system was brought to room temperature and reacted for 2 hours. After the reaction was complete, dichloromethane was added to dilute the reaction system, and the reaction was terminated with saturated sodium bicarbonate aqueous solution. The organic phase was then washed with water, washed with saturated brine, dried over anhydrous sodium sulfate, filtered, and concentrated under reduced pressure. The crude product obtained after concentration was purified by silica gel column chromatography (2:1, petroleum ether-ethyl acetate) to give a white solid compound S-7 (807 mg, 90%). Structural identification of compound S-7: R f =0.43 (1:1, petroleum ether-ethyl acetate); 1 H NMR (400MHz, CDCl3) δ7.52–7.48(m,2H),7.43–7.36(m,4H),7.36–7.27(m,4H),5.55(d,J=5.4Hz,1H),4.99(d,J=11 .3Hz,1H),4.78(d,J=11.2Hz,1H),4.23–4.15(m,1H),3.90–3.85(m,1H),3.78(d,J=3.8Hz,2H),3.70–3.63(m,2H); 13 C NMR (100MHz, CDCl3) δ137.9,133.1,132.7,129.3,128.9,128.4,128.3,128.1,87.4,81.7,75.6,72.4,71.0,63.9,62.2; HRMS (ESI): m / z calcd forC 19 H 21 N3O4S[M+Na] + :410.1151,found:410.1153.

[0109] Synthesis of compound S-8

[0110] S-7 (1.2 g, 3.1 mmol) was dissolved in pyridine (31 mL), and TBDPSCl (1.61 mL, 6.2 mol) and DMAP (38 mg, 0.31 mmol) were added under ice bath conditions. The reaction mixture was brought to room temperature and reacted for 4 hours. After the reaction was complete, methanol was added to quench the reaction. The crude product was concentrated under reduced pressure and purified by silica gel column chromatography (15:1, petroleum ether-ethyl acetate) to give a colorless syrupy compound S-8 (1.63 g, 84%). Structural identification of compound S-8: R f =0.40 (8:1, petroleum ether-ethyl acetate); 1 H NMR (400MHz, CDCl3) δ7.75–7.67(m,4H),7.49–7.34(m,14H),7.26–7.24(m,2H),5.55(d,J=5.4Hz,1H),4.96(d,J=11.0Hz,1H),4.90 (d,J=11.1Hz,1H),4.30–4.22(m,1H),3.96–3.85(m,3H),3.85–3.77(m,1H),3.70(dd,J=10.3,8.6Hz,1H),2.61(s,1H),1.08(s,9H); 13 C NMR (100MHz, CDCl3) δ138.1,135.8,135.7,133.8,133.1,132.9,132.2,130.0,130.0,129.2,128.8,12 8.4,128.2,128.0,127.9,127.9,87.4,81.5,75.6,72.8,72.1,64.2,63.7,27.0,26.7; HRMS(ESI):m / z calcdfor C 35 H 39 N3O4SSi[M+Na] + :648.2329,found:648.2330.

[0111] Synthesis of Compound 21

[0112] S-8 (1.16 g, 1.86 mmol) was dissolved in dichloromethane (18.6 mL), followed by the addition of levulinic acid (0.29 mL, 2.78 mmol), EDC·HCl (427 mg, 2.23 mmol), and DMAP (45 mg, 0.37 mmol). The reaction was carried out at room temperature for 6 hours. After the reaction was complete, the reaction system was diluted with dichloromethane. The organic phase was washed with water, then with saturated brine, dried over anhydrous sodium sulfate, filtered, and concentrated under reduced pressure. The crude product obtained after concentration was purified by silica gel column chromatography (15:1, petroleum ether-ethyl acetate) to give a white solid compound 21 (966 mg, 72%). The structure of compound 21 was identified as: R f =0.30 (8:1, petroleum ether-ethyl acetate); 1H NMR(400MHz, CDCl3)δ7.71–7.62(m,4H),7.54–7.47(m,2H),7.41–7.23(m,11H),7.23–7 .14(m,3H),5.61(d,J=5.5Hz,1H),5.26–5.12(m,1H),4.83(d,J=11.1Hz,1H),4.69(d,J= 11.1Hz,1H),4.42–4.32(m,1H),3.94(dd,J=10.3,5.4Hz,1H),3.85–3.72(m,2H),3.68( dd,J=11.7,2.3Hz,1H),2.58–2.49(m,2H),2.37–2.28(m,2H),2.07(s,3H),1.03(s,9H); 13 C NMR (100MHz, CDCl3) δ205.7,171.2,137.5,135.7,135.6,133.6,133.2,133.1,131.6,129.6,129.5,129.0,128.4,128 .1,127.9,127.6,127.5,127.5,87.0,79.4,75.1,71.9,70.4,63.7,62.4,37.6,29.7,27.8,26.7,19.2; HRMS(ESI):m / z calcd for C 40 H 45 N3O6SSi[M+Na] + :746.2696,found:746.2700.

[0113] Synthesis Example 5

[0114] Synthesis of Compound 6

[0115] Kdo donor 8b [1] (283 mg, 0.51 mmol) and receptor 9 (141 mg, 0.34 mmol) were dissolved in dry acetonitrile (11.3 mL), and activated [the drug] was added. After molecular sieve removal, the mixture was stirred at room temperature for 15 minutes. The reaction system was then placed in an ice bath and stirred for another 15 minutes. TBPA (500 mg, 0.61 mmol) was added in ten portions, maintaining the ice bath throughout the reaction, and the mixture was reacted in the dark for 5 hours. After the reaction was complete, the reaction was quenched with triethylamine. The mixture was diluted with dichloromethane, and the molecular sieve was removed by vacuum filtration. The filtrate was concentrated under reduced pressure, and the crude product was purified by silica gel column chromatography (3:1, petroleum ether-ethyl acetate) to give a colorless syrupy compound 6 (259 mg, 84%). Structure identification of compound 6: R f=0.27 (2:1, petroleum ether-ethyl acetate); 1 H NMR (400MHz, CDCl3) δ8.10–8.02(m,2H),7.58–7.50(m,1H),7.47–7.37(m,2H),5.92–5.76(m,1H),5.57(d,J=3.1Hz,1H),5.28–5.2 1(m,1H),5.19(dd,J=10.4,1.6Hz,1H),4.46–4.34(m,2H),4.23(s,1H),4.21–4.14(m,2H),4.14–3.91(m,6H),3.80(s,4H),3.75(s, 3H),3.57–3.47(m,2H),3.46–3.32(m,3H),2.54(t,J=14.3Hz,1H),2.41(dd,J=14.3,4.8Hz,1H),2.23(t,J=12.1Hz,1H),2.14(dd, J=12.6,4.6Hz,1H),1.92–1.76(m,2H),1.44(s,3H),1.38(s,3H),1.38(s,3H),1.24(s,3H),0.76(s,9H),0.10(s,3H),0.08(s,3H); 13 C NMR (100MHz, CDCl3) δ168.5,168.4,165.5,134.5,132.8,130.8,129.9,128.4,117.7,109.8,109.3,100.7,99.2,74.4,73.6,73.6,72.9,72.7 ,69.9,69.7,69.2,67.6,67.3,64.9,60.5,52.7,52.4,48.4,33.0,31. 8,28.9,27.3,27.0,25.7,25.7,25.4,17.9,-4.6,-4.6; HRMS(ESI):m / z calcd for C 43 H 65 N3O 16 Si[M+Na] + :930.4032,found:930.4030.

[0116] Synthesis of Compounds 17 and 18

[0117] Iridium complex ([Ir(COD)(PMePh2)2]PF6, 15 mg, 18 μmol) was dissolved in dry tetrahydrofuran (1.6 mL) and stirred at room temperature under hydrogen atmosphere for 30 minutes until the color changed from red to colorless to pale yellow. After exchanging the hydrogen with argon, PF6 (160 mg, 0.18 mmol) dissolved in 1.6 mL THF solution was added, and the reaction was allowed to proceed for 1 hour. After the reaction was complete, the solvent was dried under vacuum. The crude product was dissolved in acetone / H2O (3.2 mL, 4:1, v / v), and then mercuric chloride (57 mg, 0.21 mmol) and mercuric oxide (53 mg, 0.25 mmol) were added. The mixture was stirred at room temperature for 6 hours and then filtered through diatomaceous earth. The filtrate was concentrated under reduced pressure, diluted with ethyl acetate, and washed successively with 10% KI solution, water, and saturated brine. The organic layer was dried over anhydrous sodium sulfate, filtered, and concentrated under reduced pressure. The concentrated crude product was purified by silica gel column chromatography (5:1, petroleum ether-ethyl acetate) to give colorless syrupy compounds 17 (109 mg, 71%) and 18 (25 mg, 17%). Structure identification of compound 17: R f =0.30 (2:1, petroleum ether-ethyl acetate); 1 H NMR (400MHz, CDCl3) δ8.03–7.95(m,2H),7.61–7.53(m,1H),7.48–7.40(m,2H),5.54–5.48(m,1H),4.53(dd,J=3.4,1.5Hz,1H),4.41–4.35(m,1 H),4.29(q,J=6.2,6.0,6.0Hz,1H),4.22–4.16(m,1H),4.15–4.09(m,3H),4.06(dd,J=8.6,5.4Hz,1H),4.02–3.93(m,1H),3.87(s,3H),3.80(s ,3H),3.76(dd,J=8.2,6.0Hz,1H),3.62(dd,J=7.1,1.2Hz,1H),3.58–3.51(m,1H),3.48–3.37(m,3H),2.33(dd,J=13.1,4.6Hz,1H),2.21–2.10 (m,2H),1.91(t,J=12.5Hz,1H),1.87–1.79(m,2H),1.41(s,3H),1.40(s ,3H),1.38(s,3H),1.29(s,3H),0.78(s,9H),0.11(s,3H),0.09(s,3H); 13C NMR (100MHz, CDCl3) δ168.7,167.4,165.5,133.4,129.9,129.8,128.6,109.2,108.9,100.3,99.2,75.8,74.7,74.2,73.6,71.6,69 .3,66.6,66.3,65.3,65.0,60.4,53.0,52.7,48.4,37.5,36.3,29.0,26.9,26.0,25.9,25.7,25.7,18.1,-4.9,-4.9; HRMS(ESI):m / z calcd for C 40 H 61 N3O 16 Si[M+Na] + :890.3719, found:890.3718. Structure identification of compound 18: R f =0.36 (2.5:1, petroleum ether-ethyl acetate); 1H NMR (400MHz, CDCl3) δ8.13–8.04(m,2H),7.60–7.52(m,1H),7.48–7.42(m,2H),5.58(d,J=3.1Hz,1H),4.85–4.77(m,1H),4.46–4.39(m,1H) ,4.33(dd,J=3.0,1.4Hz,1H),4.32–4.24(m,2H),4.20(dd,J=9.0,6.1Hz,1H),4.13(q,J=6.4,6.4,6.4Hz,1H),4.05(dd,J=9.1,3.6Hz,1H),3 .89(dd,J=8.4,6.2Hz,1H),3.85–3.78(m,4H),3.60(dd,J=8.9,1.4Hz,1H),3.58–3.45(m,2H),3.45–3.36(m,2H),2.60–2.50(m,1H),2.50–2 .40(m,2H),2.03(dd,J=13.0,4.8Hz,1H),1.93–1.78(m,2H),1.43(s,3H),1.36(s,6H),1.24(s,3H),0.75(s,9H),0.08(s,3H),0.06(s,3H); 13C NMR (100MHz, CDCl3) δ167.6,165.4,164.0,133.1,130.2,129.9,128.6,109.9,109.2,99.1,98.4,74.0,73.8,73.3,72.6,72.0, 69.1,67.1,66.5,65.2,65.1,60.7,53.0,48.2,34.7,33.9,28.8,27.2,26.6,25.6,25.5,25.3,17.9,-4.7,-4.9; HRMS(ESI):m / z calcd for C 39 H 57 N3O 15 Si[M+Na]+:858.3457,found:858.3457.

[0118] Synthesis of Compound 19

[0119] Kdo donor 8a (521 mg, 0.98 mmol) and acceptor 17 (284 mg, 0.33 mmol) were dissolved in dry acetonitrile (10.9 mL), and activated [agent / concentrate / method] was added. After molecular sieve removal, the mixture was stirred at room temperature for 15 minutes. The reaction system was then placed in an ice bath and stirred for another 15 minutes. TBPA (962 mg, 1.18 mmol) was added in ten portions while maintaining the ice bath throughout the reaction, and the reaction was carried out in the dark for 10 hours. After the reaction was complete, the reaction was quenched with triethylamine. The mixture was diluted with dichloromethane, and the molecular sieve was removed by vacuum filtration. The filtrate was concentrated under reduced pressure, and the crude product was purified by silica gel column chromatography (3:1, petroleum ether-ethyl acetate) to give a colorless syrupy compound 19 (249 mg, 57%). Structure identification of compound 19: R f =0.27 (2:1, petroleum ether-ethyl acetate); 1H NMR(400MHz,CDCl3)δ8.13–8.06(m,4H),7.61–7.51(m,2H),7.49–7.41(m,4H),7.36–7.30(m,2H),7.26–7.21(m,2H),7.20–7.14(m,1H),5.81(d,J=2.6Hz,1H),5.59(d,J=3.2Hz,1H),4.89(d,J=11.6Hz,1H),4.59(d,J=11.6Hz,1H),4.57(s,1H),4.52–4.45(m,2H),4.26–4.11(m,4H),4.10–4.00(m,3H),4.00–3.86(m,5H),3.85(s,3H),3.79(s,3H),3.68(s,3H),3.59(dd,J=9.1,1.4Hz,1H),3.55–3.48(m,1H),3.47–3.32(m,3H),2.72(dd,J=14.5,5.1Hz,1H),2.63(dd,J=14.5,11.7Hz,1H),2.41(t,J=12.1Hz,1H),2.28–2.19(m,2H),2.15(t,J=12.3Hz,1H),1.88–1.76(m,2H),1.46(s,3H),1.43(s,3H),1.42(s,3H),1.39(s,3H),1.32(s,3H),1.25(s,3H),0.75(s,9H),0.18(s,3H),0.16(s,3H); 13 C NMR(100MHz,CDCl3)δ169.1,168.7,168.0,165.5,165.4,138.3,133.4,132.8,130.8,130.0,130.0,128.6,128.4,128.4,127.8,127.6,109.9,109.5,109.5,102.0,101.1,99.2,74.9,74.5,73.3,72.9,72.8,72.7,72.3,71.9,70.6,70.6,69.1,67.9,67.5,65.9,65.7,64.7,60.4,53.1,52.6,52.1,48.3,33.6,33.5,31.0,28.8,27.3,27.1,26.6,25.9,25.8,25.7,25.4,17.9,-4.4,-4.8;HRMS(ESI):m / z calcd for C 66 H 89 N3O 24 Si[M+Na]+ :1358.5503,found:1358.5500.

[0120] Synthesis of Compound 20

[0121] Compound 19 (250 mg, 0.20 mmol) was dissolved in dry tetrahydrofuran (5.0 mL), and triethylamine trihydrofluoric acid (0.5 mL) was added. The reaction system was heated to 50 °C and reacted overnight. After the reaction was completed, the reaction system was concentrated under reduced pressure, and the crude product obtained after concentration was purified by silica gel column chromatography (2:1, petroleum ether-ethyl acetate) to give a colorless syrupy compound 20 (199 mg, 87%). Structure identification of compound 20: R f =0.37 (1:1.5, petroleum ether-ethyl acetate); 1 H NMR (400MHz, CDCl3) δ8.17–8.10(m,2H),8.10–8.03(m,2H),7.63–7.53(m,2H),7.53–7.41(m, 4H),7.35–7.30(m,2H),7.30–7.23(m,2H),7.22–7.16(m,1H),5.80(d,J=2.7Hz,1H),5.57(d, J=2.8Hz,1H),4.86(d,J=11.6Hz,1H),4.78–4.70(m,1H),4.57(d,J=11.6Hz,1H),4.46–4.39( m,1H),4.34(s,1H),4.26–4.20(m,1H),4.20–4.14(m,3H),4.14–4.04(m,3H),4.04–3.96(m,2 H),3.96–3.88(m,2H),3.87(s,3H),3.86–3.83(m,1H),3.80(s,3H),3.65(s,3H),3.61–3.56( m,1H),3.55–3.48(m,1H),3.48–3.34(m,3H),2.85(dd,J=14.4,4.5Hz,1H),2.60(t,J=13.5Hz ,1H),2.40(t,J=12.1Hz,1H),2.36–2.27(m,2H),2.20(dd,J=12.4,4.4Hz,1H),2.07(t,J=12. 5Hz,1H),1.89–1.76(m,2H),1.48(s,3H),1.44(s,3H),1.38(s,6H),1.31(s,3H),1.24(s,3H); 13C NMR (100MHz, CDCl3) δ168.7,168.5,167.9,167.6,165.4,138.3,133.5,133.3,130.2,130.0,12 9.9,129.8,128.7,128.6,128.4,127.8,127.6,109.7,109.6,109.5,101.3,101.0,99.2,74.3,7 4.2,73.1,73.0,72.7,72.6,71.9,71.9,70.6,70.3,70.2,67.9,67.6,65.9,65.8,64.7,60.4,53 .0,52.6,52.2,48.2,33.4,33.3,29.4,28.7,27.4,27.2,26.7,25.8,25.7,25.3; HRMS(ESI):m / z calcd for C 60 H 75 N3O 24 [M+Na] + :1244.4639,found:1244.4635.

[0122] Synthesis of Compound 22

[0123] Donor 21 (100 mg, 0.14 mmol) and receptor 20 (73 mg, 0.06 mmol) were dissolved in dry toluene (1 mL), and activated [the solution] was added. After molecular sieve removal, the mixture was stirred at room temperature for 15 minutes. The reaction system was then placed in a -78°C cryogenic reactor, and NIS (44 mg, 0.19 mmol) and TfOH (1.2 μL, 13.8 μmol) were added sequentially. The reaction system was gradually heated to -10°C and reacted for 8 hours. After the reaction was complete, the reaction was quenched with triethylamine. After dilution with dichloromethane, the molecular sieve was removed by vacuum filtration. The filtrate was concentrated under reduced pressure, and the crude product was purified by silica gel column chromatography (2:1, petroleum ether-ethyl acetate) to obtain a colorless syrupy compound 22 (51 mg, 46%). Structure identification of compound 22: R f =0.26 (1:1, petroleum ether-ethyl acetate); 1H NMR(400MHz,CDCl3)δ8.19–8.14(m,2H),8.11–8.05(m,2H),7.64–7.51(m,6H),7.49–7.41(m,4H),7.37–7.29(m,7H),7.29–7.15(m,9H),5.83(d,J=3.1Hz,1H),5.81(d,J=2.5Hz,1H),5.41(t,J=9.7Hz,1H),5.29(d,J=3.4Hz,1H),4.90(d,J=11.5Hz,1H),4.71–4.60(m,2H),4.57(d,J=11.5Hz,1H),4.52(s,1H),4.46(d,J=11.1Hz,1H),4.39–4.31(m,1H),4.20–4.11(m,2H),4.11–4.02(m,4H),3.94–3.82(m,6H),3.76(s,3H),3.72–3.61(m,5H),3.59(s,3H),3.53–3.42(m,3H),3.42–3.25(m,3H),2.90(dd,J=14.4,5.0Hz,1H),2.75(t,J=13.4Hz,1H),2.60–2.49(m,1H),2.48–2.38(m,1H),2.33(t,J=12.1Hz,1H),2.28–2.09(m,5H),2.07(s,3H),1.86–1.74(m,2H),1.42(s,3H),1.40(s,3H),1.31(s,3H),1.26(s,3H),1.26(s,3H),1.16(s,3H),0.96(s,9H); 13C NMR (150MHz, CDCl3) δ206.3,170.8,169.7,168.5,167.9,165.8,165.3,138.2,138.0,136.0,135.9,133.6,133.4,133.4,133.0,130.5 ,130.0,129.7,129.6,128.6,128.5,128.4,128.4,128.2,127.8,127.7,127.7,127.6,127.6,109.8,109.7,109.5,102.2,100.8,99.2, 95.1,78.5,74.6,74.4,74.2,73.2,73.1,72.8,72.5,72.0,71.8,71.2,70.6,70.5,69.6,69.0,67.8,67.3,65.8,65.7,65.5,63.7,62.3 ,60.6,53.2,52.6,52.2,48.3,37.9,33.5,33.5,30.0,29.5,28.9,28.7,27.9,27.1,26.8,26.7,25.8,25.8,25.4,19.4; HRMS(ESI):m / z calcd for C 94 H 114 N6O 30 Si[M+Na] + :1857.7247,found:1857.7252.

[0124] Synthesis of Compound 23

[0125] Compound 22 (81 mg, 0.044 mmol) was dissolved in dry tetrahydrofuran (5.0 mL), and triethylamine trihydrofluoric acid (0.5 mL) was added. The reaction system was heated to 55 °C and reacted at this temperature for 3 days. After the reaction was completed, the reaction system was concentrated under reduced pressure, and the crude product obtained after concentration was purified by silica gel column chromatography (1:1, petroleum ether-ethyl acetate) to give a colorless syrupy compound 23 (41 mg, 58%). Structural identification of compound 23: R f =0.30 (1:1.5, petroleum ether-ethyl acetate); 1H NMR(400MHz,CDCl3)δ8.24–8.13(m,2H),8.13–8.05(m,2H),7.62–7.54(m,2H),7.54–7.40(m,4H),7.40–7.32(m,2H),7.34–7.17(m,8H),5.85(d,J=2.9Hz,1H),5.79(d,J=2.2Hz,1H),5.42(d,J=4.0Hz,1H),4.96–4.84(m,2H),4.82–4.69(m,2H),4.64(d,J=11.5Hz,1H),4.60–4.42(m,3H),4.30(dd,J=8.4,5.8Hz,1H),4.28–4.21(m,1H),4.21–4.14(m,2H),4.14–3.99(m,5H),3.99–3.94(m,1H),3.94–3.91(m,1H),3.90(s,3H),3.89–3.84(m,2H),3.80(s,3H),3.79–3.74(m,1H),3.71–3.66(m,1H),3.66(s,3H),3.64–3.56(m,2H),3.52–3.44(m,2H),3.44–3.30(m,3H),3.09(dd,J=14.5,4.5Hz,1H),3.01(dd,J=10.4,4.2Hz,1H),2.95–2.87(m,1H),2.86–2.76(m,1H),2.52–2.44(m,1H),2.41–2.31(m,2H),2.29–2.16(m,2H),2.16–2.05(m,4H),1.88–1.75(m,2H),1.53(s,3H),1.45(s,3H),1.43(s,3H),1.38(s,3H),1.32(s,3H),1.22(s,3H); 13C NMR (100MHz, CDCl3) δ206.4,172.7,169.9,168.5,168.0,165.7,165.3,138.3,138.2,133.4,133.2,130.2,130.0,130. 0,128.6,128.6,128.5,128.4,127.8,127.7,127.6,127.6,110.5,109.6,109.4,102.4,101.3,99.1,93.6,78.5,75.1,7 4.9,74.7,73.4,73.0,72.7,72.6,72.2,71.9,71.7,71.0,70.6,70.5,69.0,67.9,66.6,66.1,65.5,64.2,63.8,61.4,60 .5,53.6,52.7,52.2,48.2,37.7,33.6,33.2,31.8,29.5,28.8,27.8,26.7,26.5,26.5,26.3,25.9,25.1; HRMS(ESI):m / z calcd for C 78 H 96 N6O 30 [M+Na] + :1619.6069,found:1619.6075.

[0126] Synthesis of Compound 24

[0127] Dissolve 23 (64 mg, 0.040 mmol) in CH2Cl2 / H2O (0.26 mL, v / v, 2:1), and stir vigorously in an ice bath. Then add TEMPO (2 mg, 0.013 mmol) and BAIB (32 mg, 0.10 mmol) sequentially, maintaining the reaction in an ice bath for 5 hours. After the reaction is complete, add saturated sodium sulfite and saturated sodium bicarbonate aqueous solutions to terminate the reaction. Dilute with dichloromethane, wash the organic phase with water and saturated brine, dry with anhydrous sodium sulfate, filter, and concentrate under reduced pressure. Dissolve the crude product obtained after concentration in DMF (0.26 mL), and add K2CO3 (17 mg, 0.12 mmol) and iodomethane (15 μL, 0.24 mmol) at 0 °C. After warming the reaction system to room temperature, react for 1 hour. After the reaction is complete, add methanol to terminate the reaction. Dilute with dichloromethane, wash the organic phase with water, wash with saturated brine, dry with anhydrous sodium sulfate, filter, and concentrate under reduced pressure. The crude product obtained after concentration was purified by silica gel column chromatography (1.5:1, petroleum ether-ethyl acetate) to give a colorless syrupy compound 24 (43 mg, 66%). Structure identification of compound 24: R f=0.26 (1:1, petroleum ether-ethyl acetate); 1 H NMR (400MHz, CDCl3) δ8.20–8.15(m,2H),8.13–8.08(m,2H),7.62–7.55(m,2H),7.53–7. 43(m,4H),7.38–7.32(m,2H),7.32–7.18(m,8H),5.86(d,J=2.9Hz,1H),5.81(d,J=2.6H z,1H),5.49(d,J=3.5Hz,1H),5.05(t,J=9.4Hz,1H),4.90(d,J=11.5Hz,1H),4.84–4.74 (m,1H),4.71(d,J=11.4Hz,1H),4.65–4.53(m,3H),4.47–4.38(m,2H),4.23–3.98(m,8H) ,3.98–3.81(m,8H),3.80(s,3H),3.67(s,3H),3.60–3.56(m,1H),3.54(s,3H),3.52–3. 47(m,1H),3.45–3.31(m,4H),3.15(dd,J=14.4,4.7Hz,1H),2.84(t,J=13.7Hz,1H),2.6 6–2.58(m,1H),2.54–2.46(m,1H),2.38(t,J=12.0Hz,1H),2.34–2.13(m,5H),2.12(s,3 H),1.86–1.76(m,2H),1.44(s,3H),1.41(s,6H),1.39(s,3H),1.32(s,3H),1.29(s,3H); 13C NMR (100MHz, CDCl3) δ206.1,171.5,169.8,168.6,168.4,168.0,165.7,165.3,138.3,137.9,133.4,133.2,130.2,130.1, 130.0,128.6,128.6,128.5,128.4,127.9,127.8,127.8,127.6,109.9,109.7,109.5,102.4,101.0,99.2,94.3,77.3,75. 0,74.4,74.4,73.0,72.9,72.8,72.7,72.1,72.0,71.7,70.6,70.5,69.5,69.1,68.1,67.7,66.0,65.7,65.0,62.9,60.5, 53.6,52.6,52.6,52.2,48.3,37.6,33.5,33.4,31.8,30.0,28.7,27.6,27.1,26.8,26.7,25.8,25.7,25.3; HRMS(ESI):m / z calcd forC 79 H 96 N6O 31 [M+Na] + :1647.6018,found:1647.6031.

[0128] Synthesis of Compound 3

[0129] Compound 24 (31 mg, 0.019 mmol) was dissolved in dichloromethane (3.8 mL), and TFA / H2O (9:1, v / v, 0.38 mL) was added at 0 °C. The reaction mixture was brought to room temperature and reacted for 30 minutes. After the reaction was complete, dichloromethane was added to dilute the mixture, and the reaction was terminated with saturated sodium bicarbonate solution. The organic phase was then washed with water, saturated brine, dried over anhydrous sodium sulfate, filtered, and concentrated under reduced pressure. The crude product obtained after concentration was purified by silica gel column chromatography (40:1, dichloromethane-methanol) to give a colorless syrupy compound. The obtained compound was dissolved in CH3OH / H2O (v / v, 2:1, 3.0 mL), and 1 mol / L NaOH aqueous solution (1.0 mL) was added under ice bath conditions. The reaction mixture was brought to room temperature and reacted for 12 hours. After the reaction was complete, the mixture was analyzed using an Amberlite IR120 H2O filter. +The pH was adjusted to 8 using cation exchange resin. The mixture was filtered, and the filtrate was dried under reduced pressure. The crude product was dissolved in t-BuOH / H2O (2:1, v / v, 3.0 mL), and Pd(OH)2 / C (20 mg) was added. The mixture was reacted in a hydrogen atmosphere for 8 hours. After the reaction was complete, the mixture was filtered, and the filtrate was lyophilized. The crude product was then purified by size exclusion chromatography (BioGel P-2; eluent: 0.05 M NH4HCO3). The fraction containing the product was lyophilized to give a white, foamy product 3 (9 mg, 52% over three steps). Structure identification of compound 3: R f Not equal to 0.24 (3:2, MeOH-H2O); 1 H NMR(400MHz,D2O)δ5.14(d,J=3.4Hz,1H),4.48–4.43(m,1H),4.39–4.33(m,2H),4.30(s,1H),4.18–4.12(m,1 H),4.08–4.00(m,3H),4.00–3.89(m,4H),3.89–3.80(m,3H),3.71–3.62(m,3H),3.62–3.45(m,4H),3.35–3.2 5(m,1H),3.23–3.14(m,1H),3.10–3.00(m,1H),2.81(dd,J=10.0,3.5Hz,1H),2.49(dd,J=13.7,4.6Hz,1H),2 .24–2.11(m,2H),2.08(dd,J=13.1,4.7Hz,1H),2.05–1.93(m,2H),1.93–1.83(m,1H),1.75(t,J=12.7Hz,1H); 13 C NMR(150MHz,D2O)δ176.5,176.4,175.9,175.0,102.7,100.6,100.2,95.8,73.8,73.8,72.9,72.8,72.6,72.1,72.0,70 .9,70.1,69.9,69.1,68.0,66.6,65.5,63.4,63.1,62.9,62.7,62.1,54.8,38.9,34.6,34.4,32.0,26.2; HRMS(ESI):m / z calcd forC 33 H 54 N2O 27 [MH] - :909.2836,found:909.2854.

[0130] In summary, the synthesis steps of compound 3 are as follows: 1) Using compound 9 and compound 8b as starting materials, compound 6 is obtained by glycosylation reaction; 2) Compound 6 is obtained by deallylation reaction; 3) Compound 17 and compound 8a are obtained by glycosylation reaction; 4) Compound 19 is obtained by desilication reaction; 5) Compound 20 and compound 21 are obtained by glycosylation reaction; 6) Compound 22 is obtained by desilication reaction; 7) Compound 23 is obtained by TEMPO oxidation reaction and methyl esterification reaction; 8) Compound 24 is obtained by deisopropylidene ketalization reaction, saponification reaction and catalytic hydrogenation reduction reaction.

[0131] Synthesis Example 6

[0132] Synthesis of Compound 25

[0133] Kdo donor 7 (327 mg, 0.50 mmol) and acceptor 12 (198 mg, 0.25 mmol) were dissolved in dry acetonitrile (8.3 mL), and activated [agent / concentrate / method] was added. After molecular sieve removal, the mixture was stirred at room temperature for 15 minutes. The reaction system was then placed in an ice bath and stirred for another 15 minutes. TBPA (489 mg, 0.60 mmol) was added in ten portions while maintaining the ice bath throughout the reaction, and the mixture was reacted in the dark for 10 hours. After the reaction was complete, the reaction was quenched with triethylamine. The mixture was diluted with dichloromethane, and the molecular sieve was removed by vacuum filtration. The filtrate was concentrated under reduced pressure, and the crude product was purified by silica gel column chromatography (4:1, petroleum ether-ethyl acetate) to give a colorless syrupy compound 25 (215 mg, 62%). Structure identification of compound 25: R f =0.48 (2:1, petroleum ether-ethyl acetate); 1H NMR(400MHz,CDCl3)δ8.23–8.16(m,2H),8.07–8.00(m,2H),7.61–7.51(m,2H),7.49–7.40(m,4H),5.88–5.75(m,1H),5.68–5.59(m,1H),5.59–5.51(m,1H),5.26–5.18(m,1H),5.18–5.12(m,1H),4.66(s,1H),4.56(d,J=2.6Hz,1H),4.50–4.41(m,2H),4.39–4.29(m,1H),4.26(s,1H),4.20(dd,J=8.8,6.0Hz,1H),4.17–4.03(m,4H),4.03–3.87(m,4H),3.80(s,3H),3.69(s,3H),3.65(s,3H),3.62(dd,J=9.2,1.5Hz,1H),3.55–3.47(m,3H),3.42–3.34(m,3H),2.93(t,J=13.3Hz,1H),2.84–2.71(m,2H),2.55(dd,J=12.9,4.5Hz,1H),2.30(t,J=12.2Hz,1H),2.13(dd,J=12.5,4.3Hz,1H),1.87–1.76(m,2H),1.37(s,6H),1.35(s,3H),1.32(s,3H),1.06(s,9H),0.94(s,9H),0.84(s,9H),0.01(s,3H),-0.01(s,3H); 13 C NMR(100MHz,CDCl3)δ168.5,168.1,167.4,166.9,165.8,134.8,133.3,133.0,130.7,130.4,130.3,129.7,128.5,128.4,117.5,109.9,109.4,100.8,100.7,99.3,75.0,74.5,73.2,73.0,72.7,71.5,71.2,70.5,69.8,69.6,69.6,68.2,68.1,66.9,66.2,60.4,52.7,52.4,52.2,48.4,31.4,30.2,29.8,27.7,27.6,27.3,27.1,27.1,26.2,25.5,25.3,22.2,21.7,18.6,-5.2,-5.4;HRMS(ESI):m / z calcd for C 67 H 99 N3O 24Si2[M+Na] + :1408.6055,found:1408.6050.

[0134] Synthesis of Compound 26

[0135] Compound 25 (37 mg, 0.027 mmol) was dissolved in dry tetrahydrofuran (0.5 mL), and triethylamine trihydrofluoric acid (0.05 mL) was added under ice bath conditions. The reaction mixture was brought to room temperature and reacted for 8 hours. After the reaction was complete, the reaction mixture was concentrated under reduced pressure. The crude product obtained after concentration was purified by silica gel column chromatography (30:1, dichloromethane-methanol) to give a colorless syrupy compound. The obtained compound was dissolved in dichloromethane (0.5 mL), and TFA / H₂O (9:1, v / v, 0.1 mL) was added at 0 °C. The reaction mixture was brought to room temperature and reacted for 30 minutes. After the reaction was complete, the reaction mixture was diluted with dichloromethane, and the reaction was terminated with saturated sodium bicarbonate aqueous solution. The organic phase was then washed with water, washed with saturated brine, dried over anhydrous sodium sulfate, filtered, and concentrated under reduced pressure. The crude product was dissolved in pyridine (0.5 mL), and acetic anhydride (36 μL, 0.38 mmol) and DMAP (1 mg, 0.009 mmol) were added. The reaction was carried out overnight at room temperature. After the reaction was completed, methanol was added to terminate the reaction. The crude product was concentrated under reduced pressure, and then purified by silica gel column chromatography (2:1, petroleum ether-ethyl acetate) to give a colorless syrupy compound 26 (23 mg, 64%). The structure of compound 26 was identified as R. f =0.32 (1:1, petroleum ether-ethyl acetate); 1H NMR(600MHz,CDCl3)δ8.25–8.15(m,2H),7.95–7.87(m,2H),7.62–7.56(m,1H),7.55–7.45(m,3H),7.42–7.35(m,2H),5.84–5.76(m,1H),5.62(d,J=2.9Hz,1H),5.61–5.56(m,1H),5.41–5.35(m,1H),5.34–5.29(m,1H),5.26–5.14(m,3H),5.14–5.09(m,1H),4.85(dd,J=12.3,2.3Hz,1H),4.61–4.54(m,3H),4.51(s,1H),4.49–4.45(m,1H),4.37(d,J=8.8Hz,1H),4.27(dd,J=12.3,4.4Hz,1H),4.19(dd,J=12.3,3.2Hz,1H),4.01–3.95(m,3H),3.94–3.89(m,1H),3.87–3.84(m,1H),3.82(s,3H),3.78(s,3H),3.68–3.63(m,1H),3.58(s,3H),3.48–3.34(m,3H),2.61(dd,J=13.6,4.5Hz,1H),2.55(t,J=12.9Hz,1H),2.48(dd,J=12.7,4.7Hz,1H),2.25–2.14(m,3H),2.11(s,3H),2.06(s,3H),2.04(s,3H),2.04(s,3H),2.00(s,3H),1.95(s,6H),1.88–1.78(m,2H); 13 C NMR(150MHz,CDCl3)δ171.0,170.6,170.6,170.4,170.2,170.2,170.2,168.3,167.9,167.1,166.8,165.4,134.4,133.6,133.2,130.2,129.9,129.7,129.6,128.6,128.5,117.7,100.5,100.3,99.3,73.1,71.5,70.8,70.5,70.3,69.7,69.6,69.4,69.1,69.0,68.8,66.9,65.1,62.5,62.3,61.6,60.6,52.8,52.8,52.6,48.5,34.4,31.8,30.5,29.1,21.3,21.1,20.9,20.9,20.9,20.8,20.7;HRMS(ESI):m / z calcd for C61 H 75 N3O 31 [M+Na] + :1368.4283,found:1368.4286.

[0136] Synthesis of Compounds 27 and 28

[0137] Iridium complex ([Ir(COD)(PMePh2)2]PF6, 5 mg, 6 μmol) was dissolved in dry tetrahydrofuran (0.15 mL) and stirred at room temperature under hydrogen atmosphere for 30 minutes until the color changed from red to colorless to pale yellow. After exchanging the hydrogen with argon, 26 (26 mg, 0.019 mmol) dissolved in 0.15 mL THF solution was added, and the reaction was allowed to proceed for 1 hour. After the reaction was complete, the solvent was dried under vacuum. The crude product was dissolved in acetone / H2O (0.3 mL, 4:1, v:v), and then mercuric chloride (6 mg, 22 μmol) and mercuric oxide (6 mg, 26 μmol) were added. The mixture was stirred at room temperature for 6 hours and then filtered through diatomaceous earth. The filtrate was concentrated under reduced pressure, diluted with ethyl acetate, and washed successively with 10% KI solution, water, and saturated brine. The organic layer was dried over anhydrous sodium sulfate, filtered, and concentrated under reduced pressure. The concentrated crude product was purified by silica gel column chromatography (1:1, petroleum ether-ethyl acetate) to give colorless syrupy compounds 27 and 28 (21 mg, 1:1, 84%). Structure identification of compound 27: R f =0.49 (1:2, petroleum ether-ethyl acetate); 1H NMR (400MHz, CDCl3) δ8.17–8.10(m,2H),7.88–7.82(m,2H),7.62–7.54(m,1H), 7.54–7.42(m,3H),7.42–7.33(m,2H),5.63–5.56(m,1H),5.55(s,1H),5.44–5.3 2(m,2H),5.32–5.26(m,1H),5.13–5.08(m,1H),4.80(d,J=2.4Hz,1H),4.77–4.7 0(m,2H),4.53–4.47(m,2H),4.37–4.23(m,1H),4.21–4.10(m,1H),4.10–4.03(m ,1H),4.03–3.94(m,2H),3.92(dd,J=9.4,1.5Hz,1H),3.84(s,3H),3.74(s,3H) ,3.73(s,3H),3.69–3.66(m,1H),3.62–3.59(m,1H),3.50–3.34(m,3H),2.54–2. 43(m,1H),2.40–2.25(m,2H),2.25–2.15(m,3H),2.14(s,3H),2.11(s,3H),2.07 (s,3H),2.05(s,3H),2.04(s,3H),1.99(s,3H),1.98(s,3H),1.86–1.77(m,2H); 13 C NMR (150MHz, CDCl3) δ170.9,170.7,170.6,170.2,170.2,170.1,169.9,168.2,167.7,167.4,16 6.5,165.1,133.7,133.2,130.2,129.8,129.6,129.3,128.7,128.5,100.4,99.8,99.1,73.9,7 3.6, 73.1, 70.5, 70.4, 70.3, 70.0, 68.8, 68.3, 68.2, 66.7, 65.5, 65.0, 62.0, 61.4, 60.5, 53.4, 53.2, 52.8, 48.3, 36.1, 29.8, 29.5, 29.1, 21.2, 21.1, 21.1, 21.0, 21.0, 20.8, 20.8. Structure identification of compound 28: R f =0.51 (1:2, petroleum ether-ethyl acetate); 1H NMR(400MHz,CDCl3)δ8.18–8.11(m,2H),7.95–7.87(m,2H),7.61–7.54(m,1H),7.54–7.43(m,3H),7.42–7.35(m,2H),5.72–5.60(m,2H),5.41–5.32(m,2H),5.27–5.21(m,1H),5.17–5.10(m,1H),4.91–4.80(m,2H),4.68(s,1H),4.61(dd,J=9.3,1.4Hz,1H),4.52(dd,J=12.1,2.4Hz,1H),4.44(dd,J=12.4,2.3Hz,1H),4.40(d,J=9.6Hz,1H),4.32–4.24(m,2H),4.17(dd,J=12.5,3.5Hz,1H),4.08(dd,J=9.1,1.5Hz,1H),3.89(dd,J=12.1,5.2Hz,1H),3.82(s,3H),3.71–3.62(m,1H),3.57(s,3H),3.50–3.36(m,3H),2.68–2.55(m,2H),2.47(dd,J=12.4,4.4Hz,1H),2.36–2.25(m,2H),2.23–2.15(m,1H),2.13(s,3H),2.13(s,3H),2.08(s,3H),2.06(s,6H),1.96(s,3H),1.89(s,3H),1.87–1.79(m,2H); 13 C NMR(100MHz,CDCl3)δ170.8,170.6,170.5,170.3,170.3,170.2,170.0,167.1,166.3,166.0,165.1,163.3,133.5,133.1,130.1,130.0,129.7,129.5,128.6,128.4,100.3,98.5,97.9,73.6,71.7,70.2,70.0,69.4,68.4,68.4,68.4,68.1,66.9,65.1,64.3,62.6,61.6,61.6,60.7,53.0,52.9,48.3,34.9,33.9,31.3,28.9,21.2,21.2,20.9,20.9,20.9,20.7,20.6;HRMS(ESI):m / z calcd forC 57 H 67 N3O 30 [M+Na] +:1296.3707,found:1296.3710.

[0138] Synthesis of Compound 4

[0139] Compounds 27 and 28 (18 mg, 1:1, 0.014 mmol) were dissolved in CH3OH / H2O (v / v, 2:1, 1.5 mL), and 0.5 mL of 1 mol / L NaOH aqueous solution was added under ice bath conditions. The reaction mixture was brought to room temperature and allowed to react for 12 hours. After the reaction was complete, the analytes were analyzed using an Amberlite IR120 H2O analyzer. + The pH was adjusted to 8 using a cation exchange resin. The mixture was filtered, and the filtrate was dried under reduced pressure. The crude product was dissolved in t-BuOH / H₂O (2:1, v / v, 1.5 mL), and Pd(OH)₂ / C (20 mg) was added. The mixture was reacted in a hydrogen atmosphere for 3 hours. After the reaction was complete, the mixture was filtered, and the filtrate was freeze-dried. The crude product was then purified by size exclusion chromatography (BioGel P-2; eluent: 0.05 M NH₄HCO₃). The fraction containing the product was freeze-dried to give a white, foamy product 4 (8 mg, 78%). Structure identification of compound 4: R f =0.30(6:1,MeOH-H2O); 1 H NMR(600MHz,D2O)δ4.34–4.27(m,1H),4.27–4.22(m,1H),4.12(s,1H),4.09(s,1H),4.08–3.99 (m,4H),3.98–3.89(m,4H),3.83–3.72(m,4H),3.66(dd,J=11.8,5.7Hz,1H),3.62–3.54(m,2H), 3.36–3.27(m,1H),3.20–3.11(m,1H),3.09–2.99(m,1H),2.28(dd,J=12.7,3.6Hz,1H),2.24(d d,J=12.8,4.4Hz,1H),1.99(dd,J=12.5,4.3Hz,1H),1.96–1.84(m,4H),1.80(t,J=12.5Hz,1H); 13C NMR (150MHz, D2O) δ175.5,173.7,173.7,102.1,102.0,100.4,73.7,73.1,72.6,72.1,71.8,70.5,69. 7,69.0,66.7,65.7,65.5,65.2,62.3,62.3,62.0,61.8,38.5,36.7,35.8,35.0,26.3; HRMS(ESI):m / z calcd for C 27 H 45 NO 22 [MH] - :734.2355,found:734.2372.

[0140] In summary, the synthesis steps of compound 4 are as follows: 1) Using compounds 9 and 7 as starting materials, compound 5 is obtained by glycosylation reaction; 2) Compound 5 is successively subjected to desilication and isopropyl ketal reaction to obtain compound 12; 3) Compound 12 and compound 7 are subjected to glycosylation reaction to obtain compound 25; 4) Compound 25 is successively subjected to desilication, isopropyl ketal, and peracetylation reaction to obtain compound 26; 5) Compound 26 is subjected to deallyl reaction to obtain compound 27 and compound 28; 6) Compound 27 and compound 28 are subjected to saponification reaction and catalytic hydrogenation reduction reaction to obtain compound 4.

[0141] In other embodiments of the present invention, different synthetic techniques and methods are employed.

[0142] The four oligosaccharide molecules synthesized in this invention are as follows: Figure 2a As shown, the four oligosaccharide molecules are Figure 1 The structural fragment of the target molecule (i.e., the core hexasaccharide within the lipopolysaccharide of Acinetobacter baumannii ATCC 17904 serum type) is shown in the dashed box. The yield calculation formula for this invention is as follows:

[0143] Synthesis Example 7:

[0144] The synthetic route for the key intermediate disaccharide is as follows: Figure 3 .

[0145] Compound 7 is from reference 2.

[0146] The synthetic route for C5-OH compound 9 is as follows: Figure 7 .

[0147] Compound S-1 underwent deprotection of the TBS protecting group with the aid of TBAF, followed by removal of the benzoyl group at the C5 position with sodium methoxide, yielding compound S-2 in two steps with an 85% yield. Compound S-2 was then selectively allylated at C-4OH, yielding compound 9 in 87% yield. Compound S-1 is derived from reference 1.

[0148] Compounds 7 and 9 underwent glycosylation catalyzed by TBPA to give 2,5-linked Kdo disaccharide compound 5 in 80% yield. On one hand, after removing the 8'-O-TBS and 5',7'-O-DTBS protecting groups from disaccharide compound 5 in Et3N-3HF, and then protecting the 7',8'-OH group with isopropyl acetal, the two steps yielded 5'-OH disaccharide compound 12 in 73% yield. On the other hand, after removing the 4-O-All group from disaccharide compound 5 in the presence of an activated iridium complex and mercuric oxide and mercuric chloride, 4-OH disaccharide compound 10 (75% yield) and disaccharide compound 11 (13% yield) were obtained.

[0149] Synthesis Example 8:

[0150] The synthetic route for α-Kdo-(2→5)-α-Kdo-(2→5)-α-Kdo linear trisaccharide 4 is as follows: Figure 4 .

[0151] The 5'-OH disaccharide compound 12 was glycosylated with compound 7 to give Kdo trisaccharide 25 in 62% yield. After removal of the silyl and isopropyl protecting groups, Kdo trisaccharide 25 was reacted with acetic anhydride in pyridine to give compound 26, with an overall three-step yield of 64%. After removal of the 4-allyl group from compound 26, compounds 27 and 28 were given (overall yield 84%, 27:28 = 1:1). A mixture of compounds 27 and 28 was subjected to saponification to remove all ester protecting groups, followed by catalytic hydrogenation reduction to convert the azide group to an amino group, yielding the target linear trisaccharide 4 in two steps with a yield of 78%.

[0152] Synthesis Example 9:

[0153] The synthetic routes for α-Kdo-(2→5)-[α-Kdo-(2→4)]-α-Kdo branched trisaccharide 1 and α-Kdo-(2→5)-α-Kdo-(2→5)-[α-Kdo-(2→4)]-α-Kdo branched tetrasaccharide 2 are as follows: Figure 5 .

[0154] From reference 1.

[0155] 4-OH disaccharide compound 10 was glycosylated with compound 8a to give Kdo branched trisaccharide 13 in 70% yield. Kdo branched trisaccharide 13 was deprotected by 8'-O-TBS and 5',7'-O-DTBS protecting groups to give compound 14 (87% yield). Compound 14 was further purified by removing isopropyl acetal under acidic conditions, removing all ester protecting groups via saponification, and removing the benzyl protecting group via catalytic hydrogenation reduction while converting the azide group to an amino group, resulting in a three-step overall yield of the target branched trisaccharide 1 in 58% yield.

[0156] Compound 14 reacted with 2,2-dimethoxypropane, protecting the 7',8'-OH group with isopropyl ketal, yielding compound 15 in 86% yield. Compound 15, with its 5'-OH group acting as an acceptor, underwent glycosylation with compound 7 catalyzed by TBPA, yielding tetrasaccharide 16 in 50% yield. Tetrasaccharide 16 underwent a four-step deprotection process: removal of the 8"-O-TBS and 5",7"-O-DTBS protecting groups under Et3N-3HF; removal of the isopropyl ketal group under acidic TFA conditions; removal of all ester protecting groups via saponification; and removal of the benzyl protecting group via catalytic hydrogenation reduction, simultaneously converting the azide group to an amino group, yielding the target branched tetrasaccharide 2 in an overall four-step yield of 44%.

[0157] Synthesis Example 10:

[0158] The synthetic route for α-GlcNA-(1→4)-α-Kdo-(2→5)-[α-Kdo-(2→4)]-α-Kdo branched tetrasaccharide 3 is as follows: Figure 6 .

[0159] From reference 1.

[0160] The synthetic route for compound 21 is as follows: Figure 8 .

[0161] Compound S-3 reacted with thiophenol in the presence of boron trifluoride diethyl ether to give S-4 in 80% yield. S-4 underwent complete acetyl removal in sodium methoxide / methanol, followed by reaction with PhC(OCH3)2 to give compound S-5, protected at C4,6 by benzyl acetal, in two steps with 65% yield. Compound S-5 was then protected at C4 with a benzyl group to give S-6 in 87% yield, followed by removal of the benzyl acetal protecting group at C4,6 under acidic conditions with TFA to give compound S-7 in 90% yield. S-7 reacted with TBDPSCl to selectively protect the C-6 position with TBDPS, giving S-8 in 84% yield. S-8 reacted with LevOH to give compound 21 in 72% yield. S-3 is from reference 3.

[0162] C5-OH compound 9 and compound 8b undergo glycosylation under TBPA catalysis to give 2,5-linked Kdo disaccharide compound 6 in 84% yield. Disaccharide compound 6 is then deglycosylated with an activated iridium complex and mercuric oxide and mercuric chloride to remove 4'-O-All, yielding 4'-OH disaccharide compound 17 (71% yield) and disaccharide compound 18 (17% yield). 4'-OH disaccharide compound 17 undergoes glycosylation to give Kdo branched trisaccharide 19 in 57% yield. Trisaccharide 19 is deglycosylated with Et3N-3HF to remove 4'-O-TBS, yielding compound 20 in 87% yield. Compound 20, acting as an acceptor, undergoes glycosylation with compound 21 under NIS / TfOH catalysis to give tetrasaccharide 22 in 46% yield. Tetrasaccharide 22 was deprotected from 6”'-O-TBDPS under Et3N-3HF to give compound 23 in 58% yield. Compound 23 was then subjected to TEMPO and BAIB to oxidize the primary hydroxyl group at C6”' to a carboxyl group, which was subsequently protected by a methoxy group, yielding compound 24 in two steps in 66% yield. Compound 24 was then deprotected in three steps: removal of isopropyl acetal under acidic TFA conditions, removal of all ester protecting groups by saponification, and removal of the benzyl protecting group by catalytic hydrogenation reduction while converting the azide group to an amino group, yielding the target branched tetrasaccharide 3 in an overall three-step yield of 52%.

[0163] In other embodiments of the present invention, methods and routes for synthesizing key intermediate products are provided.

[0164] Synthesis Example 11

[0165] Synthesis of compounds S-10 and S-11

[0166] Potassium ferricyanide (K3Fe(CN)6) (5.81 g, 17.6 mmol), potassium osmium tetroxide dihydrate (K2OsO42H2O) (54 mg, 0.147 mmol), and potassium carbonate (2.68 g, 19.4 mmol) were added to a mixed solution of tert-butanol (29 mL) and water (29 mL). Compound S-9 (2.06 g, 5.88 mmol), dissolved in toluene (5 mL), was added dropwise at 0 °C, and the reaction mixture was stirred at 0 °C for 36 hours. After the reaction was complete, sodium sulfite (10 g) was added, and the mixture was stirred for another 15 minutes. The mixture was then extracted with ethyl acetate, the organic layer was washed with 1 mol / L KOH aqueous solution, dried over anhydrous sodium sulfate, filtered, and concentrated under reduced pressure. The crude product obtained after concentration was purified by silica gel column chromatography (2:1, petroleum ether-ethyl acetate) to obtain colorless syrupy compounds S-10 (1.47 g, 65%) and S-11 (0.34 g, 15%).

[0167] Structural identification of compound S-10: R f =0.30 (1.5:1, petroleum ether-ethyl acetate); 1 H NMR (400MHz, CDCl3) δ7.39–7.29(m,5H),5.55(s,1H),4.98(d,J=11.3Hz,1H) ,4.64(d,J=11.3Hz,1H),4.32(t,J=6.3Hz,1H),4.20(d,J=5.7Hz,1H),4.06(d d,J=9.9,6.3Hz,1H),3.88(q,J=4.9,4.7,4.7Hz,1H),3.76–3.61(m,3H),3.5 3(s,1H),2.78–2.51(m,2H),1.54(s,3H),1.37(s,3H),1.29(t,J=7.4Hz,3H); 13 C NMR (100MHz, CDCl3) δ137.2,128.6,128.3,128.2,109.6,79.7,79.5,78.3,76.6,73.2,72.8,67.7,62.8,28.1,26.4,24.1,14.2; HRMS (ESI): m / z calcd for C 19 H 28 O6S[M+Na] + The spectral data of 407.1505, found: 407.1505.S-10 are consistent with the reported data. [4] The match confirms that the C6 position in S-10 is a D-configuration.

[0168] Structural identification of compound S-11: R f =0.22 (1.5:1, petroleum ether-ethyl acetate); 1 H NMR (400MHz, CDCl3) δ7.43–7.28(m,5H),5.57(s,1H),4.93(d,J=11.2Hz,1H),4.66(d,J=11.2Hz,1H),4.30(t,J=6.4Hz,1H),4.20(d,J=5.6Hz ,1H),4.06–3.94(m,2H),3.83–3.70(m,2H),3.66(dd,J=11.2,4.4Hz,1 H),2.71–2.46(m,2H),1.54(s,3H),1.37(s,3H),1.30(t,J=7.6Hz,3H); 13C NMR (100MHz, CDCl3) δ138.2,128.6,128.3,128.0,109.7,80.4,78.6,76.6,75.9,73.4,70.0,69.7,65.0,28.2,26.6,24.7,14.5; HRMS (ESI): m / z calcd for C 19 H 28 O6S[M+Na] + :407.1505,found:407.1506.

[0169] Synthesis of compound S-12

[0170] Compound S-11 (655 mg, 1.71 mmol) was dissolved in dry methanol (34.1 mL), and dibutyltin oxide (637 mg, 2.56 mmol) was added. The mixture was heated to 90 °C and refluxed for 3 hours. After the reaction system cooled to room temperature, it was concentrated under reduced pressure. The concentrated product was dissolved in dry DMF (17.1 mL), and benzyl bromide (0.30 mL, 2.56 mmol) and cesium fluoride (518 mg, 3.41 mmol) were added. The mixture was reacted at room temperature for 16 hours. After the reaction was complete, the mixture was diluted with dichloromethane, and the reaction was terminated with saturated ammonium chloride aqueous solution. The organic phase was then washed with water, washed with saturated brine, dried over anhydrous sodium sulfate, filtered, concentrated under reduced pressure, and the crude product was purified by silica gel column chromatography (6:1, petroleum ether-ethyl acetate) to give a colorless syrupy compound S-12 (631 mg, 78%). Structural identification of compound S-12: R f =0.30 (3:1, petroleum ether-ethyl acetate); 1 H NMR (400MHz, CDCl3) δ7.41–7.28(m,10H),5.57(s,1H),4.92(d,J=11.3Hz,1H),4.67(d,J=11.3Hz,1H ),4.57(d,J=12.0Hz,1H),4.53(d,J=12.0Hz,1H),4.30(t,J=6.4Hz,1H),4.25–4.16(m,2H),3.99(d,J =10.1Hz,1H),3.84(dd,J=10.2,7.3Hz,1H),3.61(dd,J=9.5,7.5Hz,1H),3.52(dd,J=9.5,5.2Hz,1H) ,2.67–2.53(m,1H),2.53–2.40(m,1H),2.17(s,1H),1.53(s,3H),1.37(s,3H),1.24(t,J=7.5Hz,3H); 13C NMR (100MHz, CDCl3) δ138.4,138.0,128.5,128.4,128.1,127.9,127.8,127.8,109.5,80. 1,78.8,76.6,75.7,73.5,73.4,71.9,68.7,68.1,28.1,26.6,24.3,14.4; HRMS(ESI):m / z calcd for C 26 H 34 O6S[M+Na] + Spectral data of S-12 (found: 497.1974, found: 497.1971) and reported data. [5] The match confirms that the C6 position in S-11 is of L-configuration.

[0171] Synthesis of compound S-13

[0172] Compound S-10 (1.39 g, 3.62 mmol) was dissolved in dry methanol (72.4 mL), and dibutyltin oxide (1.35 g, 5.43 mmol) was added. The mixture was heated to 90 °C and refluxed for 3 hours. After the reaction system cooled to room temperature, it was concentrated under reduced pressure. The concentrated product was dissolved in dry DMF (36.2 mL), and benzyl bromide (0.64 mL, 5.43 mmol) and cesium fluoride (1.10 g, 7.24 mmol) were added. The mixture was reacted at room temperature for 16 hours. After the reaction was complete, the mixture was diluted with dichloromethane, and the reaction was terminated with saturated ammonium chloride aqueous solution. The organic phase was then washed with water, washed with saturated brine, dried over anhydrous sodium sulfate, filtered, concentrated under reduced pressure, and the crude product was purified by silica gel column chromatography (6:1, petroleum ether-ethyl acetate) to give a colorless syrupy compound S-13 (1.37 g, 80% over two steps). Structural identification of compound S-13: R f =0.43 (2.5:1, petroleum ether-ethyl acetate); 1H NMR (400MHz, CDCl3) δ7.39–7.27(m,10H),5.52(s,1H),4.92(d,J=11.3Hz,1H),4.59(d ,J=11.3Hz,1H),4.53(d,J=11.9Hz,1H),4.49(d,J=12.0Hz,1H),4.31(t,J=6.3Hz,1H) ,4.18(d,J=5.7Hz,1H),4.14–4.04(m,2H),3.70(dd,J=9.3,6.9Hz,1H),3.62–3.51(m, 2H),2.99(s,1H),2.74–2.42(m,2H),1.53(s,3H),1.36(s,3H),1.24(t,J=7.3Hz,3H); 13 C NMR (100MHz, CDCl3) δ138.3,137.9,128.6,128.5,128.3,128.0,127.9,127.7,109.6,79. 8,78.7,78.1,76.6,73.6,72.9,72.4,71.1,68.7,28.2,26.5,24.3,14.4; HRMS(ESI):m / z calcd for C 26 H 34 O6S[M+Na] + :497.1974,found:497.1973.

[0173] Synthesis of compound S-14

[0174] Compound S-13 (1.74 g, 3.67 mmol) was dissolved in dry tetrahydrofuran (36.7 mL), and Ph3P (1.92 g, 7.34 mmol), PhCOOH (896 mg, 7.34 mmol), and DIAD (1.45 mL, 7.34 mmol) were added sequentially. The reaction was carried out at room temperature for 3 hours. After the reaction was completed, the solution was concentrated under reduced pressure. The crude product obtained after concentration was purified by silica gel column chromatography (20:1, petroleum ether-ethyl acetate) to give a colorless syrupy compound S-14 (1.36 g, 64%). The structure of compound S-14 was identified as: R f =0.32 (10:1, petroleum ether-ethyl acetate); 1H NMR (400MHz, CDCl3) δ8.10–8.03(m,2H),7.56(t,J=7.5Hz,1H),7.46–7.39(m,2H),7.38–7.28(m,6H),7.25– 7.18(m,3H),7.14(t,J=7.3Hz,1H),5.84–5.76(m,1H),5.63(s,1H),4.78(d,J=10.8Hz,1H),4.58(d,J=12.0 Hz,1H),4.54(d,J=11.9Hz,1H),4.41(d,J=10.8Hz,1H),4.38–4.31(m,2H),4.22(d,J=5.7Hz,1H),3.83–3.7 1(m,2H),3.64(dd,J=10.2,6.9Hz,1H),2.73–2.43(m,2H),1.43(s,3H),1.37(s,3H),1.23(t,J=7.4Hz,3H); 13 C NMR (100MHz, CDCl3) δ165.8,138.1,137.8,133.2,130.2,130.0,128.6,128.5,128.4,128.4,127.8,127 .7,109.6,80.0,79.0,76.6,75.3,73.2,73.1,69.9,67.9,67.7,28.1,26.7,24.2,14.4; HRMS(ESI):m / z calcdfor C 33 H 38 O7S[M+Na] + :601.2236,found:601.2234.

[0175] Synthesis of compound S-15

[0176] Compound S-14 (1.31 g, 2.27 mmol) was dissolved in 80% AcOH (22 mL), and the reaction system was placed at 80 °C for 1 hour. After the reaction was completed, the solution was concentrated under reduced pressure, and the solvent was removed by azeotropic treatment twice with toluene (2 × 10 mL). The crude product was dissolved in pyridine (20 mL), and B2Cl (1.06 mL, 9.06 mmol) and DMAP (28 mg, 0.23 mmol) were added. The reaction was carried out at room temperature for 2 hours. After the reaction was completed, methanol was added to quench the reaction. After concentration under reduced pressure, the crude product was purified by silica gel column chromatography (10:1, petroleum ether-ethyl acetate) to give a colorless syrupy compound S-15 (1.37 g, 81%). Structural identification of compound S-15: R f =0.28 (5:1, petroleum ether-ethyl acetate); 1 H NMR (400MHz, CDCl3) δ8.25–8.16(m,2H),8.04–7.95(m,2H),7.93–7.85(m,2H),7.69 –7.62(m,1H),7.60–7.54(m,1H),7.51–7.41(m,3H),7.36–7.28(m,8H),7.25–7.12( m,6H),6.03–5.95(m,1H),5.79–5.67(m,2H),5.54(d,J=1.6Hz,1H),4.66–4.50(m,5 H),4.25–4.13(m,1H),3.90–3.73(m,2H),2.74–2.56(m,2H),1.28(t,J=7.4Hz,3H); 13 C NMR (100MHz, CDCl3) δ165.9,165.4,165.4,137.9,137.4,133.4,133.4,133.3,130.2,130.1,129.9,129.8,129.8,129.6,128.7,128. 7,128.6,128.5,128.5,128.5,128.0,127.8,127.7,82.1,75.5,73.6,73.3,73.2,72.6,70.5,69.6,68.2,25.3,14.7; HRMS(ESI):m / z calcd forC 44 H 42 O9S[M+Na] + :769.2448,found:769.2446.

[0177] Synthesis of compound S-16

[0178] Compound S-15 (1.14 g, 1.53 mmol) was dissolved in DCM (15.3 mL), and H2O (0.28 mL, 15.3 mmol) was added. Then, NIS (516 mg, 2.29 mmol) and TfOH (27 μL, 0.31 mmol) were added sequentially under ice bath conditions, and the reaction was allowed to proceed for 2 hours. After the reaction was complete, the reaction was quenched with triethylamine. The solution was diluted with dichloromethane, and the organic phase was washed with 10% sodium thiosulfate and saturated brine. The solution was dried over anhydrous sodium sulfate, filtered, concentrated under reduced pressure, and the crude product was purified by silica gel column chromatography (3:1, petroleum ether-ethyl acetate) to obtain the corresponding colorless hemiacetal syrup. The obtained compound was dissolved in DCM (13.4 mL), and CCl3CN (1.35 mL, 13.4 mmol) and DBU (0.40 mL, 2.69 mmol) were added under ice bath conditions. The reaction was allowed to proceed for 2 hours at room temperature. After the reaction was complete, the solution was concentrated under reduced pressure. The concentrated crude product was purified by silica gel column chromatography (5:1, petroleum ether-ethyl acetate) to give a colorless syrupy compound S-16 (917 mg, 71%). Structural identification of compound S-16: R f =0.28 (3:1, petroleum ether-ethyl acetate); 1 H NMR (400MHz, CDCl3) δ8.78(s,1H),8.22(d,J=7.7Hz,2H),7.98(d,J=7.7Hz,2H),7.90(d,J=7.7 Hz,2H),7.66(t,J=7.4Hz,1H),7.58(t,J=7.4Hz,1H),7.54–7.43(m,3H),7.39–7.27(m,8H),7. 26–7.14(m,6H),6.54(d,J=1.8Hz,1H),5.96(t,J=6.8Hz,1H),5.93–5.83(m,2H),4.67–4.54(m ,3H),4.50(d,J=12.0Hz,1H),4.46(d,J=10.0Hz,1H),4.25(t,J=9.6Hz,1H),3.89–3.73(m,2H); 13 C NMR (100MHz, CDCl3) δ165.8,165.4,165.2,160.4,137.9,137.2,133.6,133.5,133.4,130.2,130.1,129.9,129.8,129. 5,129.4,128.7,128.7,128.6,128.5,128.5,128.2,127.8,94.7,90.8,75.7,73.4,72.8,72.5,72.5,69.3,69.2,67.9.

[0179] Synthesis of compound S-17

[0180] Compound S-11 (382 mg, 0.99 mmol) was dissolved in dry DMF (5.0 mL), and 60% NaH (159 mg, 3.98 mmol) and BnBr (0.7 mL, 5.97 mmol) were added sequentially under ice bath conditions. The reaction mixture was brought to room temperature and reacted for 3 hours. After the reaction was complete, it was quenched with saturated ammonium chloride aqueous solution. The mixture was diluted with dichloromethane, washed with water and saturated brine, dried over anhydrous sodium sulfate, filtered, concentrated under reduced pressure, and the crude product was purified by silica gel column chromatography (20:1, petroleum ether-ethyl acetate) to give a white solid compound S-17 (488 mg, 87%). Structural identification of compound S-17: R f =0.25 (10:1, petroleum ether-ethyl acetate); 1 H NMR (400MHz, CDCl3) δ7.37–7.20(m,15H),5.59(s,1H),4.86(d,J=11.4Hz,1H),4.78(d,J =11.8Hz,1H),4.52(s,2H),4.47(d,J=11.8Hz,1H),4.36–4.24(m,2H),4.19(d,J=5.9Hz,1 H),4.14–4.03(m,2H),3.86(dd,J=10.0,7.0Hz,1H),3.74(dd,J=9.7,6.5Hz,1H),3.66(d d,J=9.7,5.8Hz,1H),2.68–2.38(m,2H),1.55(s,3H),1.37(s,3H),1.22(t,J=7.4Hz,3H); 13 C NMR (100MHz, CDCl3) δ138.8,138.6,138.3,128.5,128.4,128.4,128.0,127.9,127.7,127.7,127.7,10 9.6,80.2,79.1,76.7,75.7,75.7,73.8,73.6,72.5,70.9,69.6,28.1,26.6,24.3,14.5; HRMS(ESI):m / z calcd for C 33 H 40 O6S[M+Na] + :587.2444,found:587.2438.

[0181] Synthesis of compound S-18

[0182] Compound S-17 (350 mg, 0.62 mmol) was dissolved in 10 mL of 80% AcOH, and the reaction mixture was placed at 80 °C for 1 hour. After the reaction was complete, the mixture was concentrated under reduced pressure, and toluene (2 × 5 mL) was added twice for azeotropic removal of the solvent. The crude product was purified by silica gel column chromatography (3:1, petroleum ether-ethyl acetate) to give a colorless syrupy compound S-18 (309 mg, 95%). Structural identification of compound S-18: R f =0.25 (1.5:1, petroleum ether-ethyl acetate); 1 H NMR (400MHz, CDCl3) δ7.40–7.23(m,15H),5.31(s,1H),4.83(d,J=11.6Hz,1H),4.72(d,J=11.4Hz,1H),4.58–4.49(m,3H),4.44(d,J=11.5Hz,1H ),4.19–4.08(m,2H),3.97–3.92(m,1H),3.92–3.77(m,3H),3.68(dd,J= 9.8,5.5Hz,1H),2.63–2.42(m,3H),2.36(s,1H),1.22(t,J=7.4Hz,3H); 13 C NMR (100MHz, CDCl3) δ138.7,138.5,138.2,128.7,128.6,128.3,127.9,127.9,127.8,127 .8,84.2,76.1,75.4,74.3,73.7,73.1,72.9,72.8,71.6,70.8,25.0,14.8; HRMS(ESI):m / z calcd for C 30 H 36 O6S[M+Na] + :547.2131,found:547.2127.

[0183] Synthesis of compound S-19

[0184] S-18 (360 mg, 0.69 mmol) was dissolved in anhydrous DCM (6.9 mL), and triethyl orthobenzoate (0.24 mL, 1.0 mmol) and CSA (8 mg, 0.034 mmol) were added. The reaction was carried out at room temperature for 30 minutes. Thin-layer chromatography monitoring showed that the starting material was completely converted into the intermediate. Water (24 μL, 1.37 mmol) was added, and the mixture was stirred at room temperature for 1 hour. After the reaction was complete, the mixture was diluted with dichloromethane, washed with saturated sodium bicarbonate aqueous solution, washed with saturated brine, dried over anhydrous sodium sulfate, filtered, concentrated under reduced pressure, and the crude product was purified by silica gel column chromatography (6:1, petroleum ether-ethyl acetate) to give a colorless syrupy compound S-19 (371 mg, 86%). Structural identification of compound S-19: R f =0.45 (2.5:1, petroleum ether-ethyl acetate); 1 H NMR(400MHz, CDCl3)δ8.04(d,J=7.8Hz,2H),7.57(t,J=7.4Hz,1H),7.45–7.26(m,17H),5 .44(s,2H),4.95(d,J=11.7Hz,1H),4.77(d,J=11.3Hz,1H),4.61–4.53(m,3H),4.50(d,J =11.3Hz,1H),4.27–4.18(m,3H),4.11(t,J=9.3Hz,1H),3.88(dd,J=9.8,6.5Hz,1H),3.7 3(dd,J=9.8,5.4Hz,1H),2.68–2.48(m,2H),2.06(d,J=5.2Hz,1H),1.24(t,J=7.4Hz,3H); 13 C NMR (100MHz, CDCl3) δ166.3,138.9,138.5,138.2,133.4,130.1,129.9,128.6,128.6,128.6,128.5,128.0, 127.9,127.8,127.7,82.4,76.1,75.6,74.9,74.7,73.7,73.1,72.0,71.9,70.9,25.5,14.9; HRMS(ESI):m / z calcd for C 37 H 40 O7S[M+Na] + :651.2393,found:651.2396.

[0185] Synthesis of compound S-20

[0186] Donor S-16 (222 mg, 0.26 mmol) and recipient S-19 (110 mg, 0.18 mmol) were dissolved in 1.8 mL of dry DCM, and activated [agent / concentrate / method] was added. After molecular sieve removal, the mixture was stirred at room temperature for 15 minutes. The reaction system was then placed in a -78°C cryogenic reactor, and TMSOTf (4.8 μL, 26.3 μmol) was added. The reaction system was gradually heated to -30°C and reacted for 1 hour. After the reaction was complete, the reaction was quenched with triethylamine. After dilution with dichloromethane, the molecular sieve was removed by vacuum filtration. The filtrate was concentrated under reduced pressure, and the crude product was purified by silica gel column chromatography (6:1, petroleum ether-ethyl acetate) to obtain a colorless syrupy compound S-20 (200 mg, 87%). Structural identification of compound S-20: R f =0.40 (2.5:1, petroleum ether-ethyl acetate); 1 H NMR (400MHz, CDCl3) δ8.24–8.17(m,2H),8.15–8.08(m,2H),7.87–7.81(m,2H),7.81– 7.75(m,2H),7.67–7.60(m,1H),7.60–7.54(m,1H),7.54–7.48(m,1H),7.48–7.40(m,5 H),7.40–7.33(m,8H),7.32–7.27(m,6H),7.26–7.22(m,3H),7.23–7.07(m,12H),5.9 9(dd,J=8.5,4.7Hz,1H),5.74–5.67(m,2H),5.56(dd,J=2.8,1.7Hz,1H),5.45(d,J=1. 7Hz,1H),5.40(d,J=1.6Hz,1H),4.92(d,J=11.5Hz,1H),4.88(d,J=11.0Hz,1H),4.74 (d,J=12.3Hz,1H),4.62(d,J=10.4Hz,1H),4.59–4.47(m,6H),4.41–4.30(m,3H),4.28 –4.23(m,1H),4.23–4.18(m,1H),4.13–4.05(m,1H),3.99(dd,J=10.5,8.3Hz,1H),3.9 4–3.85(m,2H),3.74(dd,J=9.8,5.7Hz,1H),2.66–2.46(m,2H),1.23(t,J=7.4Hz,3H); 13C NMR (100MHz, CDCl3) δ166.0,165.3,165.0,163.6,138.6,138.4,138.1,137.9,137.7,133.4,133.3,13 3.2,133.1,130.4,130.3,130.2,129.9,129.8,129.7,129.7,129.5,128.7,128.7,128.6,128.6,128.5 ,128.4,128.4,128.3,128.3,127.9,127.8,127.8,127.7,127.7,127.5,99.7,92.0,82.4,75.5,75.4,7 5.2,74.8,74.3,73.6,73.0,72.8,72.5,72.4,71.4,70.6,70.5,69.7,69.4,25.4,14.9; HRMS(ESI):m / z calcd forC 79 H 76 O 16 S[M+Na] + :1335.4752,found:1335.4752.

[0187] Synthesis of compound S-21

[0188] Kdo donor S-20 (140 mg, 0.11 mmol) and acceptor 12 (45 mg, 0.057 mmol) were dissolved in dry acetonitrile (1.9 mL), and activated [agent / concentrate / etc.] was added. After molecular sieve removal, the mixture was stirred at room temperature for 15 minutes. The reaction system was then placed in an ice bath and stirred for another 15 minutes. TBPA (105 mg, 0.13 mmol) was added in ten portions while maintaining the ice bath throughout the reaction, and the mixture was reacted in the dark for 10 hours. After the reaction was complete, the reaction was quenched with triethylamine. The mixture was diluted with dichloromethane, and the molecular sieve was removed by vacuum filtration. The filtrate was concentrated under reduced pressure, and the crude product was purified by silica gel column chromatography (4:1, petroleum ether-ethyl acetate) to give a colorless syrupy compound S-21 (100 mg, 86%). Structural identification of compound S-21: R f =0.30 (2:1, petroleum ether-ethyl acetate); 1H NMR(400MHz,CDCl3)δ8.24–8.17(m,2H),8.06–7.97(m,4H),7.91–7.79(m,4H),7.61(t,J=7.4Hz,1H),7.54–7.33(m,13H),7.33–7.19(m,14H),7.20–7.06(m,12H),5.98–5.87(m,2H),5.85–5.79(m,2H),5.79–5.67(m,1H),5.63(t,J=2.5Hz,1H),5.56(s,1H),5.54(s,1H),5.19–5.08(m,2H),5.05(d,J=10.5Hz,1H),4.92(d,J=11.6Hz,1H),4.69–4.51(m,7H),4.51–4.41(m,3H),4.37(dd,J=10.8,4.4Hz,2H),4.34–4.20(m,4H),4.16–3.99(m,6H),3.99–3.81(m,8H),3.80(s,3H),3.74(dd,J=10.6,4.9Hz,1H),3.65–3.59(m,1H),3.55–3.49(m,1H),3.47(s,3H),3.42–3.32(m,3H),3.22(dd,J=10.6,2.1Hz,1H),2.95–2.84(m,1H),2.62(dd,J=13.9,4.4Hz,1H),2.26(t,J=12.2Hz,1H),2.10(dd,J=12.6,4.4Hz,1H),1.89–1.75(m,2H),1.47(s,3H),1.31(s,6H),1.22(s,3H); 13C NMR (100MHz, CDCl3) δ168.4,168.1,166.3,166.1,166.0,165.3,165.1,139.1,138.5,138.4,138.3,137.6,134.5,13 3.4,133.3,133.2,133.2,133.1,130.4,130.2,130.1,130.1,130.0,129.8,129.8,129.7,129.5,128.8,128.7,128.6 ,128.5,128.5,128.4,128.4,128.4,128.3,127.8,127.7,127.7,127.6,127.5,127.5,127.3,117.5,109.8,109.8,100.4,100.3,99.3,96.6,75.8,75.7,75.0,74.9,74.7,74.6,73.4,73.3,73.2,73.1,73.173.0,72.9,72.9,72.7,72.7 72.4,72.2,71.4,70.7,70.2,69.8,69.7,69.6,69.2,68.5,68.4,68.2,60.4 ,52.7,52.3,48.3,31.3,28.9,27.9,27.0,26.9,25.6,24.5; HRMS(ESI):m / z calcd for C 114 H 121 N3O 32 [M+NH4] + :2061.8277,found:2061.8269.

[0189] Synthesis of compound S-22

[0190] Compound S-21 (83 mg, 0.041 mmol) was dissolved in dichloromethane (0.8 mL), and TFA / H₂O (9:1, v / v, 0.1 mL) was added at 0 °C. The reaction mixture was brought to room temperature and reacted for 30 minutes. After the reaction was complete, the mixture was diluted with dichloromethane, and the reaction was terminated with saturated sodium bicarbonate solution. The organic phase was then washed with water, saturated brine, dried over anhydrous sodium sulfate, filtered, and concentrated under reduced pressure. The crude product was dissolved in pyridine (0.8 mL), and acetic anhydride (38 μL, 0.41 mmol) and DMAP (1 mg, 0.008 mmol) were added. The mixture was reacted overnight at room temperature, and the reaction was terminated with methanol. The crude product was concentrated under reduced pressure, and purified by silica gel column chromatography (2:1, petroleum ether-ethyl acetate) to give a colorless syrupy compound S-22 (70 mg, 81%). Structural identification of compound S-22: R f =0.28 (1:1, petroleum ether-ethyl acetate); 11H NMR (400 MHz, CDCl3) δ 8.24–8.16 (m, 2H), 8.04–7.98 (m, 2H), 7.98–7.92 (m, 2H), 7.92–7.86 (m, 2H), 7.86–7.80 (m, 2H), 7.66–7.59 (m, 1H), 7.54–7.39 (m, 7H), 7.38–7.23 (m, 12 h), 7.23–7.08 (m, 18H), 7.05–6.97 (m, 2H), 5.93 (dd, J = 9.3, 3.5 Hz, 1H), 5.87 (dd, J = 9.5, 3.0 Hz, 1H), 5.82–5.69 (m, 2H), 5.55 (d, J = 2.1 Hz, 1H), 5.46–5.40 (m, 1H), 5.35 (t, J = 2.4 Hz, 1H), 5.31 (d, J = 2.1 Hz, 1H), 5.24–5.11 (m, 4H), 5.11–5.04 (m, 1H), 4.89 (dd, J = 12.3, 2.5 Hz, 1H), 4.81 (d, J = 11.5 Hz, 1H), 4.74–4.35 (m, 11H), 4.31–4.05 (m, 9H), 4.04–3.83 (m, 5H), 3.82 (s, 3H), 3.78–3.63 (m, 3H), 3.62 (s, 3H), 3.56 (dd, J = 11.0, 3.6 Hz, 1H), 3.47–3.34 (m, 3H), 2.75–2.56 (m, 2H), 2.28 (t, J = 12.2 Hz, 1H), 2.12 (dd, J = 12.7, 4.5 Hz, 1H), 2.05 (s, 3H), 2.03 (s, 3H), 2.03 (s, 3H), 1.99 (s, 3H), 1.88–1.79 (m, 2H); 13C NMR (100MHz, CDCl3) δ171.1,170.6,170.4,170.0,168.3,167.6,166.5,166.2, 166.2,165.3,165.2,139.3,138.5,138.4,138.2,137.7,134.3,133.4,133.4, 133.2,130.5,130.2,130.1,130.0,129.9,129.8,129.8,129.7,129.4,128.7,128.6,128.6,128.5,128.5,128.5,128.5,128.4,128.4,128.3,127.8,127.7,1 27.6,127.6,127.6,127.5,127.4,127.4,117.6,100.4,99.6,99.2,97.4,75.8,75.3,75.3,74.3,73.5,73.4,73.2,73.1,72.7,72.5,72.4,72.3,72.2,71.9, 71.7,70.7,70.6,70.4,70.2,69.8,69.7,69.5,69.2,69.1,68.9,62.2,61.5,6 0.6,52.8,52.5,48.5,31.6,29.5,29.1,21.2,20.9,20.9,20.8; HRMS(ESI):m / z calcd for C 116 H 121 N3O 36 [M+Na] + :2154.7628,found:2154.7633.

[0191] Synthesis of compounds S-23 and S-24

[0192] An iridium complex ([Ir(COD)(PMePh2)2]PF6, 2 mg, 2.5 μmol) was dissolved in dry tetrahydrofuran (0.2 mL) and stirred at room temperature under hydrogen atmosphere for 30 minutes until the color changed from red to colorless to pale yellow. After exchanging the hydrogen with argon, S-22 (53 mg, 0.025 mmol) dissolved in 0.2 mL THF solution was added, and the reaction was allowed to proceed for 1 hour. After the reaction was complete, the solvent was dried under vacuum. The crude product was dissolved in acetone / H2O (0.4 mL, 4:1, v:v), and then mercuric chloride (8 mg, 30 μmol) and mercuric oxide (8 mg, 35 μmol) were added. The mixture was stirred at room temperature for 6 hours and then filtered through diatomaceous earth. The filtrate was concentrated under reduced pressure, diluted with ethyl acetate, and washed successively with 10% KI solution, water, and saturated brine. The organic layer was dried over anhydrous sodium sulfate, filtered, and concentrated under reduced pressure. The concentrated crude product was purified by silica gel column chromatography (2:1, petroleum ether-ethyl acetate) to give colorless syrupy compounds S-23 and S-24 (45 mg, 1:2, 87%). Structural identification of compound S-23: R f =0.25 (1:1, petroleum ether-ethyl acetate); 1 H NMR (400MHz, CDCl3) δ8.23–8.15(m,2H),8.05–7.96(m,2H),7.96–7.89(m,4H ),7.85–7.79(m,2H),7.66–7.59(m,1H),7.53–7.38(m,7H),7.37–6.98(m,32 H),5.99–5.89(m,1H),5.82(dd,J=9.6,3.0Hz,1H),5.79–5.72(m,1H),5.66– 5.59(m,1H),5.49–5.45(m,1H),5.41–5.29(m,2H),5.29–5.06(m,3H),4.86– 4.77(m,1H),4.76–4.52(m,6H),4.50–4.22(m,8H),4.22–4.14(m,2H),4.14– 4.04(m,3H),4.01–3.88(m,4H),3.84(s,3H),3.70(s,3H),3.70–3.50(m,3H) ,3.49–3.37(m,3H),3.15(d,J=10.3Hz,1H),2.59–2.43(m,2H),2.19–2.14(m ,1H),2.05(s,3H),2.04(s,3H),2.03(s,3H),1.98(s,3H),1.87–1.80(m,3H); 13C NMR (150MHz, CDCl3) δ170.6,170.6,170.0,168.3,166.8,166.1,165.6,165.2,165.1,138.9,138.3,138.3,138.2,137.7 ,133.2,133.2,133.1,130.4,130.1,130.1,130.0,129.7,129.7,129.7,129.6,128.6,128.2,127.8,127.8,127.8,127. 6,127.5,127.5,100.8,99.5,99.0,97.3,75.1,75.1,74.2,73.7,73.3,73.1,73.0,72.7,72.1,71.7,70.5,70.0,69.8,69.5,68.9,68.7,68.2,65.6,61.9,61.9,60.5,53.2,52.8,48.4,33.4,30.5,29.1,21.2,20.9,20.9,20.9; Structural identification of compound S-24: R f =0.28 (1:1, petroleum ether-ethyl acetate); 1H NMR(400MHz,CDCl3)δ8.22–8.16(m,2H),8.03–7.94(m,4H),7.90–7.84(m,2H),7.84–7.77(m,2H),7.62(t,J=7.4Hz,1H),7.53–7.38(m,7H),7.36–6.98(m,32H),5.91(d,J=8.5Hz,1H),5.85(dd,J=9.5,3.0Hz,1H),5.77–5.73(m,1H),5.53(s,1H),5.37–5.29(m,3H),5.21–5.08(m,3H),4.94(dd,J=12.4,2.2Hz,1H),4.85–4.76(m,2H),4.69–4.52(m,4H),4.49–4.22(m,9H),4.22–4.13(m,4H),4.13–4.04(m,3H),3.96(t,J=9.9Hz,1H),3.80(s,3H),3.70–3.47(m,5H),3.47–3.37(m,3H),2.54(dd,J=12.9,5.1Hz,1H),2.47(t,J=12.5Hz,1H),2.27–2.22(m,1H),2.20(s,3H),2.08(s,3H),2.05–2.02(m,1H),2.01(s,3H),2.00(s,3H),1.88–1.80(m,2H); 13C NMR (100MHz, CDCl3) δ170.8,170.6,170.4,169.7,166.4,166.3,166.2,1 65.3,165.3,165.1,162.6,139.4,138.6,138.4,137.7,133.4,133.1,13 0.6,130.2,130.1,130.0,129.9,129.8,129.8,129.8,129.5,128.7,128 .6,128.5,128.5,128.5,128.4,128.4,128.3,128.3,128.3,127.9,127. 8,127.6,127.4,127.4,127.3,99.4,98.5,97.9,97.2,75.4,75.2,75.2, 74.4,73.5,73.4,73.2,73.1,72.6,72.5,72.5,72.3,72.2,72.0,71.9,7 1.2,70.8,70.6,70.2,69.9,69.2,69.0,68.7,68.6,64.4,61.6,61.3,60 .7,53.0,48.3,33.9,30.5,28.9,21.3,20.9,20.8,20.5; HRMS(ESI):m / z calcd for C 112 H 113 N3O 35 [M+Na] + :2082.7053,found:2082.7058.

[0193] The synthesis of compound 29 involved dissolving compounds S-23 and S-24 (28 mg, 1:2, 0.014 mmol) in CH3OH / H2O (v / v, 2:1, 1.5 mL), and adding 0.5 mL of 1 mol / L NaOH aqueous solution under ice bath conditions. The reaction mixture was brought to room temperature and allowed to react overnight. After the reaction was complete, the solution was analyzed using an Amberlite IR120 H2O analyzer. + The pH was adjusted to 8 using a cation exchange resin. The mixture was filtered, and the filtrate was dried under reduced pressure. The crude product was dissolved in t-BuOH / H2O (2:1, v / v, 1.5 mL), and Pd(OH)2 / C (20 mg) was added. The mixture was reacted in a hydrogen atmosphere for 8 hours. After the reaction was complete, the mixture was filtered, and the filtrate was lyophilized. The crude product was then purified by size exclusion chromatography (BioGel P-2; eluent: 0.05 M NH4HCO3). The fraction containing the product was lyophilized to give a white, foamy product 29 (9 mg, 74%). Structure identification of compound 29: R f=0.30(6:1,MeOH-H2O); 1 H NMR(600MHz,D2O)δ5.20(s,1H),5.07(s,1H),4.41(dd,J=12.5,3.7Hz,1H),4.16–4.04(m,6H),4 .04–4.01(m,2H),4.01–3.94(m,4H),3.93(d,J=11.7Hz,1H),3.91–3.85(m,2H),3.80–3.74(m,3 H),3.74–3.65(m,5H),3.63–3.56(m,3H),3.35–3.30(m,1H),3.15–3.09(m,1H),3.05–2.99(m,1 H),2.30(dd,J=12.6,4.3Hz,1H),2.04–1.96(m,2H),1.95–1.85(m,2H),1.79(t,J=12.3Hz,1H); 13 C NMR (150MHz, D2O) δ175.5,173.5,102.1,101.7,101.2,100.2,76.3,75.4,73.2,72.0,72.0,71.7,71.7,70.4,70.0,69. 9,69.6,69.1,68.7,68.3,65.9,65.9,65.6,65.0,63.2,63.1,62.6,62.3,61.7,38.3,36.4,35.0,26.7; HRMS(ESI):m / z calcd for C 33 H 57 NO 27 [MH] - :898.3040,found:898.3059.

[0194] Compound 29 as Figure 11 A negative control was present.

[0195] The four oligosaccharide molecules synthesized in this invention can be conjugated with suitable proteins to form glycoconjugates, which can then be used to prepare drugs or vaccines for the treatment or prevention of Acinetobacter baumannii.

[0196] The embodiments of the present invention have been described above with reference to the accompanying drawings. However, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of the present invention without departing from the spirit and scope of the claims. All of these forms are within the protection scope of the present invention.

[0197] References

[0198] 1.W.Huang,Y.-Y.Zhou,X.-L.Pan,X.-Y.Zhou,J.-C.Lei,D.-M.Liu,Y.Chu,J.-S.Yang,J.Am.Chem.Soc.2018,140,3574-3582.

[0199] 2.J.-S.Huang,W.Huang,X.Meng,X.Wang,P.-C.Gao,J.-S.Yang,Angew.Chem.Int.Ed.2015,54,10894-10898.

[0200] 3.C.-H.Chang,LSLico,T.-Y.Huang,S.-Y.Lin,C.-L.Chang,SDArco,S.-C.Hung,Angew.Chem.Int.Ed.2014,53,9876-9879.

[0201] 4.G.Tian,J.Hu,C.Qin,L.Li,X.Zou,J.Cai,PHSeeberger,J.Yin,Angew.Chem.Int.Ed.2020,59,13362-13370.

Claims

1. A cell wall core oligosaccharide fragment of Acinetobacter baumannii, characterized in that, Compounds with the structure shown in formula (1): Equation (1).

2. A glycoconjugate characterized in that, It is composed of oligosaccharide fragments from the core of Acinetobacter baumannii cell wall as described in claim 1, conjugated with proteins.

3. An immunoassay reagent comprising the core oligosaccharide fragment of Acinetobacter baumannii cell wall as described in claim 1.

4. A method of preparing the cell wall core oligosaccharide fragment of Acinetobacter baumannii as defined in claim 1, characterized in that, The oligosaccharide fragment is a compound represented by formula (1), and includes the following steps: S1.

1. Using compounds 9 and 7 as starting materials, compound 5 was obtained by glycosylation reaction; S1.

2. Compound 5 is subjected to an allyl group removal reaction to obtain compound 10; S1.

3. Compound 10 and compound 8a are glycosylated to obtain compound 13; S1.

4. Compound 13 is subjected to a desilication reaction to obtain compound 14; S1.

5. Compound 14 is subjected to deisopropylidene ketalization, saponification and catalytic hydrogenation reduction to obtain the compound shown in formula (1); The structural formulas of compounds 9, 7, 5, 10, 8a, 13, and 14 are shown below: Compound 9; Compound 7; Compound 5; Compound 10; Compound 8a; Compound 13; Compound 14.

5. A method for preparing oligosaccharide fragments from the core of Acinetobacter baumannii cell wall, characterized in that, The oligosaccharide fragment is the compound shown in formula (2). Equation (2); Includes the following steps: S2.

1. Using compounds 9 and 7 as starting materials, compound 5 was obtained by glycosylation reaction; S2.

2. Compound 5 is subjected to an allyl group removal reaction to obtain compound 10; S2.

3. Compound 10 and compound 8a are subjected to a glycosylation reaction to obtain compound 13; S2.

4. Compound 13 is subjected to a desilication reaction to obtain compound 14; S2.

5. Compound 14 is subjected to an isopropyl ketal reaction to yield compound 15; S2.

6. Compound 15 and compound 7 are glycosylated to obtain compound 16; S2.

7. The compound 16 was subjected to desilication, deisopropyl ketalization, saponification and catalytic hydrogenation reduction reaction in sequence to obtain the compound shown in formula (2); The structural formulas of compounds 9, 7, 5, 10, 8a, 13, 14, 15, and 16 are shown below: Compound 9; Compound 7; Compound 5; Compound 10; Compound 8a; Compound 13; Compound 14; Compound 15; Compound 16.

6. A method for preparing oligosaccharide fragments from the core of Acinetobacter baumannii cell wall, characterized in that, The oligosaccharide fragment is the compound shown in formula (3). Equation (3); Includes the following steps: S3.

1. Using compound 9 and compound 8b as starting materials, compound 6 was obtained by glycosylation reaction; S3.

2. Compound 6 is subjected to an allyl group removal reaction to obtain compound 17; S3.

3. Compound 17 and compound 8a are glycosylated to obtain compound 19; S3.

4. Compound 19 is subjected to a desilication reaction to obtain compound 20; S3.

5. Compound 20 and compound 21 are subjected to a glycosylation reaction to obtain compound 22; S3.

6. Compound 22 is subjected to a desilication reaction to obtain compound 23; S3.

7. Compound 23 is subjected to TEMPO oxidation and methyl esterification to obtain compound 24; S3.

8. Compound 24 is subjected to deisopropylidene ketalization, saponification and catalytic hydrogenation reduction to obtain the compound shown in formula (3); The structural formulas of compounds 9, 8b, 6, 17, 8a, 19, 20, 21, 22, 23, and 24 are shown below: Compound 9; Compound 8b; Compound 6; Compound 17; Compound 8a; Compound 19; Compound 20; Compound 21; Compound 22; Compound 23; Compound 24.

7. A method for preparing oligosaccharide fragments from the core of Acinetobacter baumannii cell wall, characterized in that, The oligosaccharide fragment is the compound shown in formula (4). Equation (4); Includes the following steps: S4.

1. Using compounds 9 and 7 as starting materials, compound 5 was obtained by glycosylation reaction; S4.

2. Compound 5 was subjected to desilication and isopropylidene ketal reaction sequentially to obtain compound 12; S4.

3. Compound 12 and compound 7 are glycosylated to obtain compound 25; S4.

4. Compound 25 was subjected to desilication, deisopropylidene ketalization, and full acetylation reactions to obtain compound 26; S4.

5. Compound 26 is subjected to an allyl group removal reaction to yield compounds 27 and 28; S4.

6. Compounds 27 and 28 are subjected to saponification and catalytic hydrogenation-reduction to obtain the compound shown in formula (4); The structural formulas of compounds 9, 7, 5, 12, 25, 26, 27, and 28 are shown below: Compound 9; Compound 7; Compound 5; Compound 12; Compound 25; Compound 26; Compound 27; Compound 28.

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